Beetle Identification / able to retract its head

Beetle Identification / able to retract its head

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I can't find any identification of this beetle online. The closest guess I got to it is "Hister beetle" but the rough surfaces on its shell make me think otherwise.

The most common behavior is that when feeling threatened, it plays dead for some time. It retract its head, and then covers it with its 2 front limbs, which make it look like a piece of wood or a tree seed.

Here's a video showing its movement

Philippines, Southeast Asia. under tropical savanna climate

Edit: Based on Arthur J Frost's comment, Trox Beetles more likely resemble it in movement and behavior. So it's probably more like a member of Trogidae beetle family.


Histeridae is a family of beetles commonly known as clown beetles or Hister beetles. This very diverse group of beetles contains 3,900 species found worldwide. They can be easily identified by their shortened elytra that leaves two of the seven tergites exposed, and their geniculate (elbowed) antennae with clubbed ends. These predatory feeders are most active at night and will fake death if they feel threatened. This family of beetles will occupy almost any kind of niche throughout the world. Hister beetles have proved useful during forensic investigations to help in time of death estimation. Also, certain species are used in the control of livestock pests that infest dung and to control houseflies. Because they are predacious and will even eat other Hister beetles, they must be isolated when collected.

    MacLeay, 1819Bickhardt, 1914Reitter, 1909Marseul, 1857Gyllenhal, 1808Fowler, 1912MacLeay, 1819Blanchard, 1845Bickhardt, 1914Marseul, 1857Bickhardt, 1913

Beetle Identification / able to retract its head - Biology

How to Identify Terrestrial Gastropods


It may be difficult, even for malacologists, to identify molluscs, simply because they do not usually possess many characters that are consistently useful for distinguishing among related species. This section of the tool was designed to assist the user in becoming familiar with the common characters that are used in the identification of terrestrial snails and slugs.

Shell Classification

How do you know if you truly have a snail or a slug?

Gastropods that possess an obvious shell are termed snails whereas gastropods that appear to lack an obvious shell are termed slugs. In the case of semi-slugs it may be debatable whether the animal should be considered a snail or a slug. The entities included in this tool are divided into two major categories (snails and slugs) to reduce ambiguity and to allow users to quickly and more efficiently navigate through the key.

Shell obvious with definite coiling and animal may be able to retract into it. Figure 1. Typical snails

Shell very reduced or internal and if present, it has no definite coiling. If the shell is partially external, it is usually small and is located on the posterior end of the mantle (see image below, far right). Figure 2. Typical slugs

Slug Characters

Several morphological characters can be used to identify slugs. A few of these include:

Mantle Characters:
  • Body covered by mantle (partly or wholly)
  • Location of breathing pore on mantle (or on the body of the animal)
  • Mantle groove
Body Characters:
  • Length (preserved specimens may shrink to approximately 70-80 % the length of living specimens)
  • Body color
  • Body markings (spots, blotches, stripes, bands)
  • Mucus pore
  • Length of the slug (fully extended at maturity)
  • Sole color
  • Tail constriction at the point of amputation (this is a faint groove that can be observed on the dorsal surface of the tail behind the mantle. A narrow dark-colored band on the sole of the animal can also represent the point of amputation.) It should be noted that the point of amputation might not always be visible in species that typically possess one.
Mucus Color:
Keel Characters:

Shell Characters

Shells generally have a large number of characters that can be used to distinguish between groups of snails. Shell sculpturing is one such character.

Common shell sculpturing include:
  • Hairs/Bristles &ndash projections on the shell that resemble mammalian hair
  • Pits &ndash regularly shaped indentation in the shell
  • Dents- irregularly shaped indentations in a shell
  • Striae &ndash groove-like indentations that follow the whorls
  • Lirae &ndash raised ridges that follow the whorls
  • Ribs &ndash raised ridges that run at an angle (usually transversely) to the whorls
  • Pleats/ Wrinkles &ndash any type of ridging or creasing that appears to have been formed by folding or crumpling

Figure 3. Shell terminology.

Common Shell Types

Figure 4. Common shell types.

How to Measure a Terrestrial Gastropod

Measurement can be a useful character in the identification of a terrestrial gastropod. In snails, the length is taken from the apex of the shell to the base of the aperture (mouth). The width should be taken at the widest part of the shell when the shell is oriented so that aperture faces the observer the width is measured from the side of the body whorl to the outermost side of the aperture (mouth). Terrestrial slugs are measured from the head, excluding the tentacles to the tip of the tail (Figure. 5). It is important that the animal is fully extended to in order to obtain an accurate measurement.


The umbilicus may be used as a diagnostic character when classifying snails. The umbilicus may be open or closed. The width of the open umbilicus is taken at the widest part of the inner surfaces of the body whorl (Figure. 6). Figure 6. Types of umbilicus commonly observed in terrestrial snails.

Counting Whorls

There are several ways to count the number of whorls on the shell of a snail. The most commonly used method described by Pilsbry (1939) will be discussed here. Before counting the whorls, an imaginary line should be drawn across the shell as demonstrated in figure 7 below. The whorls are then counted following the direction of the coils. A complete turn indicates a whorl (i.e., every time the line is intersected when following the whorls). The body whorl may not be complete, meaning that it may end in quarters or thirds (Figure 7).

Figure 7. Counting shell whorls.


The genitalia (formed by the fusion of both male and female structure) are one of the most diagnostic characters used to distinguish between mollusc species. In many groups (e.g., Veronicellids), a positive identification cannot be obtained without the use of the genitalia characters. A generalized diagram of the genitalia can be found in Figure 8. There may also be reproductive structures that are present in some species and not others. Additional information on the genitalia (structure and function) can be found in the biology section of this tool. Figure 8. Generalized diagram of a terrestrial mollusc’s reproductive system.

Beetle Identification / able to retract its head - Biology

Nearly 500 species of Passalidae have been described, mainly in the new world tropics (Arnett et al. 2002). The family Passalidae, commonly known as bess bugs or patent leather beetles, is a member of the superfamily Scarabaeoidea, and has only a few occurring species within the United States (Schuster 1983). The horned passalus or betsy beetle, Odontotaenius disjunctus (Illiger), is a widely distributed, easily recognizable beetle and is the most commonly encountered beetle of Passalidae in the United States, due to its relative monopoly in the North American geography. Previously, Passalus punctiger (Lepeletier) and Passalus punctatostriatus (Percheron) have been reported as exotic species in the United States, but recent records do not indicate a current population of either species (Schuster 1983). Species within the family Passalidae, including the horned passalus, are beneficial decomposers of wood. The horned passalus only decomposes decaying wood or logs, and it is not a pest of urban structures.

Figure 1. Lateral view of a horned passalus, Odontotaenius disjunctus Illiger. The shiny black color was responsible for another commonly used name: patent leather beetle. Photograph by Lyle J. Buss, University of Florida.

Odontotaenius floridanus Schuster, a beetle of close ancestry to O. disjunctus, occurs endemically in a limited area in Florida. Odontotaenius floridanus resembles O. disjunctus in most aspects of the life cycle and morphology except for having wider front tibiae and a reduced horn (Schuster 1994). Few members of Passalidae are established in the United States, and only the two species mentioned previously are believed not to have migrated or been introduced from Central America (Schuster 1983).

Synonymy (Back to Top)

Odontotaenius disjunctus has also been formerly known as Popilius disjunctus (Illiger) and Passalus cornutus (Fabricius) (Hincks 1951).

Horned passalus is the approved Entomological Society of America common name, but the following common names are often also associated with it: betsy beetle, bess bug, patent leather beetle, Jerusalem beetle, horn beetle, and peg beetle. Some of these common names apply specifically to O. disjunctus, and others may generally refer to the family Passalidae.

Distribution (Back to Top)

The horned passalus occurs in a wide range from mid-Florida to Massachusetts, Southern Texas to Minnesota, and Nebraska (Schuster 1983). More recent sources indicate further expansion from eastern Texas, throughout the eastern United States, and from southern Manitoba through the Canadian deciduous forests, and southern Ontario (Arnett et al. 2002).

Figure 2. United State's distribution of the horned passalus, Odontotaenius disjunctus Illiger. (Map was extrapolated using literature sources Schuster 1983 and Arnett et al. 2002). Programmed by Mike Boone Christopher S. Bibbs, University of Florida.

Description (Back to Top)

Adults: Horned passalus adults are relatively large, dark glossy black beetles, with adult size typically ranging from 30&ndash40 mm (1.2 inch&ndash1.6 inch). Golden hairs can be seen lining the middle pair of legs, pronotum, and antennae. These hairs are detectable by the naked eye.

Figure 3. Golden hair fringes on a horned passalus, Odontotaenius disjunctus Illiger. Photograph by Christopher S. Bibbs, University of Florida.

The elytra, or hardened outer forewing, are characterized by deep grooves. The horned passalus also has a groove down the midline of the pronotum.

Figure 4. Dorsal view of an adult horned passalus, Odontotaenius disjunctus Illiger. Photograph by Lyle J. Buss, University of Florida.

Antennae have 10 segments, with the distal three segments forming a lamellate club. This is an easily identifiable characteristic of the family.

Figure 5. Close up of lanellate antennae, a characteristic of the horned passalus, Odontotaenius disjunctus Illiger. Photograph by Christopher S. Bibbs, University of Florida.

A single, curved horn points forward on top of the head and between the eyes. Adults of the horned passalus additionally have thick, robust mandibles that clearly are also visible.

Figure 6. Close up of the head and curved horn of the horned passalus, Odontotaenius disjunctus Illiger. Also notice the fringes of golden hairs and the mites just behind the head. Photograph by Lyle J. Buss, University of Florida.

On average, adults live up to a year. A key characteristic of horned passalus adults is the acoustical signals (stridulation) they emit when disturbed or agitated.

Eggs: The eggs of the horned passalus are exceptionally large, measuring at 3.0 by 2.4 mm (approximately 0.1 inch) when first laid and reaching 3.7 by 3.2 mm just before hatching. The size of the eggs makes them easy to manipulate in the large mandibles of the adults. Eggs are typically found in groups surrounded by frass from the adults.

Larvae: The larvae are large, white grubs that have up to three instars. Larvae are found in the same galleries as the adults. To obtain nutrients, the larvae feed on predigested wood from the adults.

Figure 7. Larva of the horned passalus, Odontotaenius disjunctus Illiger, posed to see body shape. Photograph by Lyle J. Buss, University of Florida.

Figure 8. Larva of the horned passalus, Odontotaenius disjunctus Illiger, with close up of head capsule. Photograph by Lyle J.Buss, University of Florida.

Figure 9. Larva of the horned passalus, Odontotaenius disjunctus Illiger, with close up of legs. Photograph by Lyle J.Buss, University of Florida.

Grubs appear to only have two pairs of legs, but a third pair is present and reduced. Only the first two pairs are used for locomotion. As is typical for beetles within the superfamily Scarabaeoidae, grubs retain a characteristic C-shaped posture when not active. The larvae have no active defenses except for well proportioned mandibles, and auditory signals similiar to those used by adult beetles.

Pupae: As pupae begin to form, they become pearly white with a rainbow sheen. As the pupae age, they lose their rainbow sheen and can range in color from off white to earth-toned. Pupae that are nearing emergence become translucent. Pupation times vary based on climatic conditions.

Figure 10. Pupa of the horned passalus, Odontotaenius disjunctus Illiger. Photograph by Shelly Cox, Missouri Department of Conservation.

Life Cycle and Biology (Back to Top)

Using its large mandibles, the horned passalus cuts into fallen logs and creates galleries where it lives and breeds.

Figure 11. Deeply carved wood tunnels of the horned passalus, Odontotaenius disjunctus Illiger. (University of Florida educational specimens). Photograph by Christopher S. Bibbs, University of Florida.

Adults aggregate and compete for sections of fallen wood, provided the wood is large enough to support more than the initial inhabitants of the wood.

Figure 12. Aggregation of the horned passalus, Odontotaenius disjunctus Illiger, in the same wood pieces. (University of Florida educational specimens). Photograph by Christopher S. Bibbs, University of Florida.

Parents of new egg clutches will create a subsocial relationship where adults of both sexes tend the larva throughout the gallery complex in cooperative care of brood (Schuster and Schuster 1985). If the wood remains undisturbed, more than one generation will cohabitate the same log and young adults will also participate in sibling and new brood care. Adults are territorial and protect their galleries from intruders, but both adults and larvae will cannibalize injured immatures (King and Fashing 2007). Mites can commonly be found on the exoskeleton of the horned passalus. These mites are diverse, but not harmful to humans or the beetle.

Once eggs have been laid, adults move clutches of eggs through their galleries repeatedly. Searching for the best areas of wood for larvae to settle, parents of the eggs will attempt to find and guard ideal feeding sites for the protection and transportation of their eggs (Wicknick and Miskelly 2009). Once eggs hatch, larvae remain with the parent adults and share mixtures of frass and softened wood. Depending upon temperature and moisture conditions, the entire life cycle may occur within a summer season or take as long as 14&ndash16 months (Kraus and Ryan 1953).

Prior to pupation, adults will pack the pupal chamber cells within the decayed wood with detritus and remnants. These pupal cells disguise the vulnerable stage within, but the full purpose of these cells has not been proven (Valenzuela-Gonzalez 1992). Adults of all ages, including young newly emerged adults have the ability to create these pupal cells. The quality of the cells varies with the age of the adult. Should these detritus cells around the pupae become damaged, adults will repair them. Pupae are capable of overwintering if the additional time is necessary for full development.

While some logs may maintain multiple generations of beetle, young adults typically stay within the parent log for a minimal period of time. Overlapping generations of beetles within the same host structure will only remain as long as it takes them to fully mature. These young adults lack the characteristic black shell of the species, and instead have a red coloration when they emerge from the pupal stage. This red color slowly darkens to black, at which point the insect is considered a mature adult (Schuster and Schuster 1985).

Figure 13. Freshly emerged teneral adult horned passalus, Odontotaenius disjunctus Illiger, already inhabited by mites (crawling on elytra). Photograph by Shelly Cox, Missouri Department of Conservation.

This newly mature adult will leave the parent log and participate in a nuptial flight, one of the only instances of their wing use (MacGown and MacGown 1996). During observations of the nuptial flight, adults were found to be susceptible to light attractants such as light traps and street lights. At the end of the nuptial flight adults will seek out a new log to start another aggregation.

The gentle nature of the horned passalus and its reluctance to fly has contributed to its adoption as a safe and easy-to-handle creature for live specimen demonstrations and outreach education by universities. Domestically, it is low maintenance in care and only requires consistent supplies of moistened wood which can be obtained in any natural area that is normally suitable for the beetle.

Feeding Habitat (Back to Top)

The horned passalus prefers hardwoods, such as oak (Quercus spp.) or elm (Ulmus spp.), and will only reside in a log that has fallen and begun to decay. Optimal conditions include high moisture levels, as the beetles are sensitive to dry conditions. For the beetles to digest the wood, the wood must also have microflora, such as naturally occurring fungi and bacteria, which are breaking down the wood. These microflora aid in the predigestion of the wood.

In plant feeding insects, undigested remains are expelled in the form of a fine powdery material, called frass. When the horned passalus takes up residence in a log, the beetles facilitate log decomposition by chewing up wood pulp and expelling frass. Fungi and bacteria then target frass for their own nutrient extraction (Arnett et al. 2002). Once the frass has been sufficiently reprocessed by the fungi and bacteria, the horned passalus then consumes the frass and wood again for successful digestion. Logs that have been inhabited by the horned passalus tend to have sawdust littered around and beneath the log.

Sounds (Back to Top)

Several members of the family Passalidae have the ability to stridulate. Other groups of insects have also developed this capacity, including but not limited to various species of crickets, katydids, grasshoppers, ants and cicadas. Insect stridulation is the emission of sounds by creating friction between two body segments or limbs. Stridulation can be simply demonstrated by taking a plastic comb and scraping the edge of your nail down the row of comb teeth. Stridulation is common as a form of communication within a species, similar in specificity to pheromones and photic signals in insects.

In the horned passalus both adults and larvae have the ability to create clearly audible sounds using stridulation. The horned passalus specifically has 17 discovered sound signals among adults and larvae, all of which are for communication within their complex subsocial aggregations including for defense, group communication, and management of immature beetles (Schuster 1975). As expressed by Reyes-Castillo and Jarman (1980), this repertoire "represents the most elaborate system of sound communication known for any arthropod."

Adults create auditory signals using an adapted abdomen and wing structure. The non-hardened hind wings, which are kept folded beneath the protective elytra, have many rows of small spines on the underside. On the abdominal segments beneath these spined areas of the hind wings is a toughened region called pars stridens. This structure is not identifiable to the unaided eye.

Figure 14. Elytra raised, exposing the dorsal throax and abdomen of a pinned and dried horned passalus, Odontotaenius disjunctus Illiger. Photograph by Christopher S. Bibbs, University of Florida.

To create sound, the spines are scraped across this textured area of the abdomen. Different frequencies of noise can be generated depending on the speed and pattern of the movement (Reyes-Castillo and Jarman 1983).

In immature horned passalus, the third pair of legs is actually reduced in order to aid stridulation. The middle pair of legs has pars stridens (a set of ridges) on the proximal end of the leg. The third pair of legs, with its reduced radial movement, is able to reach the pars stridens with its apex and create the friction necessary to generate noise. The larval auditory signals are equivocal in volume to the adult signal.

Figure 15. Close up of one of the reduced third pair of legs in a larvae of the horned passalus, Odontotaenius disjunctus Illiger. Photograph by Lyle J.Buss, University of Florida.

The tips of these reduced legs have multiple teeth close to the apex of the leg point. These various teeth are used at different angles to create the different frequencies necessary to communicate between larvae, parent adults, and non-parent adults.

The stridulations of the horned passalus show evidence that even outside of the protective logs, they serve defensive purposes. The larvae and fully developed beetles have few defenses against predators. However, their readiness to sound off when disturbed contributes to their survival.

In experiments testing the importance of their sound making as a defense, larvae of the horned passalus were intentionally exposed to crows to observe predation. The length of time until mortality was much greater among larvae that actively emitted sounds (Buchler et al. 1981).

Selected References (Back to Top)

  • Arnett Jr RH, Thomas MC, Skelley PE, Frank JH. (editors) 2002. American Beetles, Volume II: Polyphaga: Scarabaeoidea through Curculionoidea. pp. 861. CRC Press, Boca Raton, FL.
  • Buchler ER, Wright TB, Brown ED. 1981. On the functions of stridulation by the passalid beetle Odontotaenius disjunctus (Coleoptera: Passalidae). Animal Behaviour 29: 483-486.
  • Hincks WD. 1951. A note on "Passalus cornutus Fabricius" (Passalidae). The Coleopterists Bulletin 5: 12-13.
  • King A, Fashing N. 2007. Infanticidal behavior in the subsocial beetle Odontotaenius disjunctus (Illiger) (Coleoptera: Passalidae). Journal of Insect Behavior 20: 527-536.
  • Kraus JB, Ryan MT. 1953. The stages of development in the embryology of the horned passalus beetle, Popilius disjunctus (Illiger). Annals of the Entomological Society of America 46: 1-20.
  • MacGown JA, MacGown MJ. 1996. Observation of a nuptial flight of the horned passalus beetle, Odontotaenius disjunctus (Illiger) (Coleoptera: Passalidae). The Coleopterists Bulletin 50: 201-203.
  • Reyes-Castillo P, Jarman M. 1983. Disturbance sounds of adult passalid beetles (Coleoptera: Passalidae): structural and functional aspects. Annals of the Entomological Society of America 76: 6-22.
  • Reyes-Castillo P, Jarman M. 1980. Some notes on larval stridulation in neotropical Passalidae (Coleoptera: Lamellicornia). The Coleopterists Bulletin 34: 263-270.
  • Schuster JC. 1994. Odontotaenius floridanus new species (Coleoptera: Passalidae): a second U.S. passalid beetle. Florida Entomologist 77: 474-479.
  • Schuster JC. 1983. The Passalidae of the United States. The Coleopterists Bulletin 37: 302-305.
  • Schuster JC. 1975. Comparative Behaviour, Acoustical Signals, and Ecology of New World Passalidae (Coleoptera). 127 pages. PhD Thesis. University of Florida, Gainesville, FL.
  • Schuster JC, Schuster LB. 1985. Social behavior in passalid beetles (Coleoptera: Passalidae): cooperative broode care. Florida Entomologist 68: 266-272.
  • Valenzuela-Gonzalez JV. 1992. Pupal cell-building behavior in passalid beetles (Coleopter: Passalidae). Journal of Insect Behavior 6: 33-41.
  • Wicknick JA, Miskelly SA. 2009. Behavioral interactions between non-cohabitating bess beetles, Odontotaenius disjunctus (Illiger) (Coleoptera: Passalidae). The Coleopterists Bulletin 63: 108-116.

Authors: Christopher S. Bibbs, Amanda C. Hodges, Rebecca W. Baldwin, University of Florida
Photographs: Christopher S. Bibbs and Lyle J. Buss, University of Florida Shelly Cox, Missouri Department of Conservation
Map: Mike Boone Christopher S. Bibbs, University of Florida
Audio file: Rebecca Baldwin and Christopher Bibbs, University of Florida
Web Design: Don Wasik, Jane Medley
Publication Number: EENY-487
Publication Date: December 2010. Latest revision: October 2013

How to Manage Pests

Red turpentine bark beetle frass at base of Monterey pine.

Bark beetles, family Scolytidae, are common pests of conifers (such as pines) and some attack broadleaf trees. Over 600 species occur in the United States and Canada with approximately 200 in California alone. The most common species infesting pines in urban landscapes and at the wildland-urban interface in California are the engraver beetles, the red turpentine beetle, and the western pine beetle (See Table 1 for scientific names). In high-elevation landscapes, such as the Tahoe Basin area or the San Bernardino Mountains, the Jeffrey pine beetle and mountain pine beetle are also frequent pests of pines. Two recently invasive species, the Mediterranean pine engraver and the redhaired pine bark beetle, colonize various Mediterranean pines, which are widely planted in and around the Los Angeles Basin and the Central Valley.

Cedar and cypress bark beetles attack arborvitae, cypress, false cypress, junipers, and redwoods. The fir engraver attacks white and red fir at high-elevation locations. Oak bark and ambrosia beetles attack oaks and certain other broadleaf trees including California buckeye and tanbark oak. A long-time (naturalized) invasive bark beetle called the shothole borer attacks damaged branches and trunks of many broadleaved tree species, including fruit trees and English laurel. Two other invasive species, the European elm bark beetle and the banded elm bark beetle feed on elms and vector Dutch elm disease fungus (Ophiostoma novo-ulmi). In its native habitat in Asia, the banded elm bark beetle reportedly also feeds on certain non-elm tree species.

California now has 20 invasive species of bark beetles, of which 10 species have been discovered since 2002. The biology of these new invaders is poorly understood. For more information on these new species, including illustrations to help you identify them, see the USDA Forest Service pamphlet, Invasive Bark Beetles (PDF) .

Other common wood-boring pests in landscape trees and shrubs include clearwing moths, roundheaded borers, and flatheaded borers. Certain wood borers survive the milling process and may emerge from wood in structures or furniture including some roundheaded and flatheaded borers and woodwasps. Others colonize wood after it has been placed in structures, such as carpenter ants, carpenter bees, powderpost beetles, and termites. For more information on these other borers, see the Pest Notes listed in References.


Bark beetle adults are small, cylindrical, hard-bodied insects about the size of a grain of rice. Most species are dark red, brown, or black. When viewed under magnification, their antennae are visibly elbowed with the outer segments enlarged and clublike. When viewed from above, the head is partly or completely hidden by the pronotum (the top of the body part behind the head). Bark beetles have strong mandibles (jaws) for chewing. A buckshot pattern of holes is apparent on the bark surface of infested branches or trunks where the new adults have emerged. Larvae of most species are off-white, robust, grublike, and may have a dark brown head.

Identifying Bark Beetles by their Damage and Signs

The species of tree attacked and the location of damage on the tree help in identifying the bark beetle species present (Table 1). On large pines, for example, engraver beetles usually attack trees near the top, whereas red turpentine beetles attack the lower portion of the trunk. They can even colonize near the root collar and exposed roots and continue to mine under the bark below ground on the large roots. Engraver beetles are dark brown, cylindrical, and have a scooplike depression at the end of the abdomen that is lined with stout spines. Their presence is indicated by piles of dry boring dust pushed out on the bark surface. Red turpentine beetles are larger than engraver beetles, reddish brown, and have a rounded tip to the abdomen. Their presence is indicated by large, pinkish brown to white pitch tubes (a mixture of pine sap and beetle boring dust that appears on the lower trunk).

Table 1. Bark Beetles Common in California Landscapes.
Species Trees affected Generations per year Comments
Cedar and cypress bark beetles (Phloeosinus species) arborvitae, cypress, false cypress (Chamaecyparis), junipers, and redwood 1 to 2 tunnels resemble centipede on wood surface and the inner bark adults feed on and kill twigs egg-laying female attracted to trunk of dead or dying trees
Elm bark beetles (Scolytus multistriatus, Scolytus schevyrewi 1 ) elms 2 overwinter as fully grown larvae in bark shot holes in bark indicate damage lay eggs in limbs and trunk of injured, weakened, or recently cut elms spread Dutch elm disease fungi
Engraver beetles (Ips emarginatus, Ips mexicanus, Ips paraconfusus, Ips pini, Ips plastographus) pines 1 to 5 overwinter as adults often make wishbone-shaped tunnels attack pines near the top of the stem
Fir engraver
(Scolytus ventralis)
white and red fir 1 to 2 overwinter as larvae adults excavate deep and long, two-armed galleries across the grain of the sapwood
Jeffrey pine beetle (Dendroctonus jeffreyi) Jeffrey pine 1 to 2 attack midtrunk of large trees, from 5 to about 30 ft make long J-shaped galleries, overwinter as larvae in the inner bark
Mediterranean pine engraver (Orthotomicus [formerly Ips] erosus) 1 pine 3 to 4 infest trunk and large limbs of Mediterranean pines, especially Aleppo pine (Pinus halepensis) and Italian stone pine (Pinus pinea)
Mountain pine beetle (Dendroctonus ponderosae) pine, frequently on lodgepole and sugar pine 1 to 2 attack midtrunk of large trees, from 5 to about 30 ft makes long J-shaped galleries, overwinter as larvae in the inner bark
Oak ambrosia beetles (Monarthrum species) Oak bark beetles (Pseudopityophthorus species) buckeye, oaks, and tanbark oak 2 or more overwinter beneath bark bleeding, frothy, bubbling holes with boring dust indicate damage attack stressed trees
Redhaired pine bark beetle (Hylurgus ligniperda) 1 pine 2 to 3 believed to prefer roots and lower trunk of declining Aleppo pine and Canary Island pine (Pinus canariensis)
Red turpentine beetle (Dendroctonus valens) pines, rarely in larch, spruce, or white fir 0.5 to 2 attack lowest 2 to 8 ft. of trunk and the large roots pitch tubes appear on bark overwinter as adults and larvae rarely kill trees
Shothole borer (Scolytus rugulosus) English laurel, fruit trees, hawthorn, and other woody plants 2 or more infestation indicated by gumming of woody parts, appearance of boring dust, or twig dieback remove and destroy infested parts
Twig beetles (Pityophthorus carmeli, Pityophthorus juglandis, Pityophthorus nitidulus, Pityophthorus setosus) pine, walnut 2 or more attack lateral shoots and twigs, can mine the pith pine species are associated with pitch canker disease transmission on walnut Pityophthorus juglandis is associated with thousand cankers disease transmission
Western pine beetle (Dendroctonus brevicomis) Coulter and ponderosa pines 2 to 4 attack midtrunk, then spread up and down larvae feed on inner bark, complete development in outer bark attack in conjunction with other pests
1 Recently introduced species whose biology and potential impact in California is poorly understood.

Identifying Bark Beetles by their Galleries

Peeling off a portion of infested bark to reveal the winding pattern of the beetle galleries (tunnels chewed by adults and larvae) is a good way to identify individual beetle species. Red turpentine beetle and western pine beetle adults usually pack about 60% of their egg-laying galleries with a sawdustlike boring dust called &ldquofrass,&rdquo whereas engraver beetles maintain clean, open adult galleries. Red turpentine beetle adults mine out wide cavelike galleries that progress down along the stem. Their larvae feed as a group in generally the same direction as the gallery. Western pine beetle adults tunnel back and forth across the stem in a gallery pattern that looks like a piece of spaghetti. Their larvae feed individually in mines that lead away from the adult gallery. Engraver beetle adults make shorter, compact gallery patterns that are made up of 3 to 4 egg galleries emerging from an open cell in the center. The larvae feed individually in mines much like the western pine beetle. Galleries chewed by larvae of all species are packed with frass.


Bark beetle females lay small, oval, whitish eggs just beneath the outer bark. After the eggs hatch, the tiny larvae mine galleries that branch out from the egg-laying gallery. At first the larval mines are very narrow, but they gradually increase in diameter as the larvae grow. Pupation occurs within or beneath the bark in enlarged chambers at the ends of the larval tunnels. Pupae are usually plump and whitish. Adults can emerge at any time of year, if they are fully developed and the temperatures are high, but emergence is most common in late spring and again in late summer to early fall. After emergence, adults may re-infest the same tree or, in most cases, disperse to attack susceptible trees elsewhere. Most bark beetle species have two or more generations a year in California, depending on temperature. At warmer locations (such as lower elevations away from the coast), the season of attack is usually longer and beetles have more generations per year in comparison with cooler coastal or high-elevation locations.


Bark beetles mine the inner bark (the phloem-cambial region) on twigs, branches, or trunks of trees and shrubs. This activity often starts a flow of tree sap in conifers, but sometimes even in hardwoods like elm and walnut. The sap flow (pitch tube) is accompanied by the sawdustlike frass created by the beetles. Frass accumulates in bark crevices or may drop and be visible on the ground or in spider webs. Small emergence holes in the bark are a good indication that bark beetles were present. Removal of the bark with the emergence holes often reveals dead and degraded inner bark and sometimes new adult beetles that have not yet emerged. Bark beetles frequently attack trees weakened by drought, disease, injuries, or other factors that may stress the tree. Bark beetles can contribute to the decline and eventual death of trees however only a few aggressive species are known to be the sole cause of tree mortality.

In addition to attacking larger limbs, some species such as cedar and cypress bark beetles feed by mining twigs up to 6 inches back from the end of the branch, resulting in dead tips. These discolored shoots hanging on the tree are often referred to as &ldquoflagging&rdquo or &ldquoflags.&rdquo Adult elm bark beetles feed on the inner bark of twigs before laying eggs. If an adult has emerged from cut logs or a portion of a tree that is infected by Dutch elm disease, the beetle&rsquos body will be contaminated with fungal spores. When the adult beetle feeds on twigs, the beetle infects healthy elms with the fungi that cause Dutch elm disease. Elms showing yellowing or wilting branches in spring may be infected with Dutch elm disease and should be reported to the county agricultural commissioner.


Except for general cultural practices that improve tree vigor, little can be done to control most bark beetles once trees have been attacked. Because the beetles live in the protected habitat beneath the bark, it is difficult to control them with insecticides. If trees or shrubs are infested, prune and dispose of bark beetle-infested limbs. If the main trunk is extensively attacked by bark beetles, the entire tree or shrub should be removed. Unless infested trees are cut and infested materials are quickly removed, burned, or chipped on site, large numbers of beetles can emerge and kill nearby host trees, especially if live, unattacked trees nearby are weakened or stressed by other factors. Never pile infested material adjacent to a live tree or shrub.

Cultural Control
Tree Selection

Plant only species properly adapted to the area. Learn the cultural requirements of trees, and provide proper care to keep them growing vigorously. Healthy trees are less likely to be attacked and are better able to survive attacks from a few bark beetles. Where bark beetles have been a problem, plant nonhost trees. For instance, engraver beetles and red turpentine beetles do not attack redwoods or atlas cedars. A mixture of tree and shrub species in planted landscapes will reduce mortality resulting from bark beetles and wood borers.

Reduce Tree Stress

Pay particular attention to old, slow-growing trees, crowded groups of trees, and newly planted trees in the landscape. Large nursery stock or transplanted trees, notably oaks and pines, can become highly susceptible to bark beetles or wood borers after replanting. Transplanting success depends on the tree species and its condition, appropriate tree and site selection, characteristics of the planting site, the season of the year, the transplanting method, and follow-up care. Stresses placed on a tree caused by poor planting or planting at the wrong time of year, lack of proper care afterwards, or the planting of an inappropriate species for the site will increase a tree&rsquos susceptibility to bark beetles or wood borers.

Prevention is the most effective method of managing bark beetles and related wood-boring insects in most instances it is the only available control. Avoid injuries to roots and trunks, damage and soil compaction during construction activities, and protect trees from sunburn (sunscald) and other abiotic disorders. Irrigation may be important during dry summer months in drought years, especially with tree species that are native to regions where summer rain is common. Also, dense stands of susceptible trees should be thinned (complete removal of some of the trees) to increase the remaining trees&rsquo vigor and ability to withstand an attack.

Irrigate when appropriate around the outer canopy, not near the trunk. Avoid the frequent, shallow type of watering that is often used for lawns. A general recommendation is to irrigate trees infrequently, such as twice a month during drought periods. However, a sufficient amount of water must be used so that the water penetrates deeply into the soil (about 1 foot below the surface). The specific amount and frequency of water needed varies greatly depending on the site, size of the tree, and whether the tree species is adapted to summer drought or regular rainfall.

Properly prune infested limbs, and remove and dispose of dying trees so that bark- and wood-boring insects do not emerge and attack other nearby trees. Timing of pruning is important avoid creating fresh pruning wounds during the adult beetles&rsquo flight season. Do not prune elm trees from March to September or pines during February to mid-October. Do not pile unseasoned, freshly cut wood near woody landscape plants. Freshly cut wood and trees that are dying or have recently died provide an abundant breeding source for some wood-boring beetles. Tightly seal firewood beneath thick (10 mil), clear plastic sheets in a sunny location for several months to exclude attacking beetles, and kill any beetles already infesting the wood. To be effective, solar/plastic treatment requires vigilance and careful execution. It is important to keep wood piles small, use high-quality clear plastic resistant to UV (ultraviolet light) degradation, and thoroughly seal edges and promptly patch holes to prevent beetles from escaping. For more information on cultural controls, see the publications by Donaldson and Seybold 1998 (PDF) and Sanborn 1996.

Biological Control

When bark beetles attack trees, natural enemies are attracted to feeding and mating bark beetles. The two main groups of natural enemies are predators and parasites. Predators are more important in regulating bark beetle populations than parasites. Natural enemies are unlikely to save an infested tree, but they can reduce bark beetle population size, thereby reducing the number of nearby trees that are attacked and killed by bark beetles. The release of predators and/or parasites into sites infested with bark beetles has not been an effective tactic to suppress bark beetle populations.

The following natural enemies attack the western pine beetle, but rarely control it: woodpeckers, several predaceous beetles such as the blackbellied clerid (Enoclerus lecontei) and a trogossitid beetle (Temnochila chlorodia), a predaceous fly (Medetera aldrichii), snakeflies, and parasitic wasps.

Behavioral Control

Bark beetles locate mates and attract or repel other individuals of the same species by emitting species-specific airborne chemicals called pheromones. Pheromones are naturally occurring chemicals that are widely used as baits to monitor bark beetles by attracting them to traps. These baits are especially important for detecting invasive species. Professional foresters have sometimes controlled or suppressed small local populations of bark beetles by using attractant pheromones in traps, and repellent pheromones and other behavioral chemicals to deter beetles from valuable trees. Some behavioral chemicals are being used experimentally on an area-wide basis to protect stands of forest trees. The interactions among host trees and beetles and their pheromones are complex and often poorly understood. Researchers are refining the reliability of pheromone-based management techniques. Behavioral chemicals are currently recommended for use only by specially trained professionals familiar with bark beetle management. Landscape professionals and home gardeners should consult with local California Cooperative Extension specialists if they are interested in this management option.

Chemical Control

Unless trees are monitored regularly so that bark beetle attack can be detected early, any chemical spray application made once the beetles have aggregated and penetrated the bark is likely to be too late and ineffective. Treatment must target the adults by spraying the bark so that beetles are killed when they land on trees and attempt to bore into the bark to lay eggs. Chemically treating trees that have been previously attacked will provide no benefit and could kill beneficial insects. Seriously infested trees, or trees that are dead or dying due to previous beetle attacks, cannot be saved with insecticide treatments and should be removed. Systemic insecticides, meaning those that are implanted or injected through the bark or applied to soil beneath trees, have not been shown to prevent attack or control populations of bark beetles. Although new systemic products are being investigated, they are not currently recommended for bark beetle control.

Circumstances for Effective Use of Insecticides

Highly valued, uninfested host trees may be protected by spraying their bark with a persistent, registered insecticide labeled as a preventive spray for bark beetles. Look for signs of recent infestation to help decide whether preventive spraying of nearby, lightly attacked or unattacked trees may be justified. Spraying a persistent insecticide on valuable, uninfested host trees near infested trees may be warranted to protect uninfested host trees from bark beetles. However, do not substitute preventive sprays for proper cultural care. The infestation status of a tree can be determined by inspecting the trunk or limbs for fresh pitch tubes or frass peeling a small portion of the outer bark from the trunk or limbs and looking for signs of adult beetles or larvae and inspecting the foliage for yellow or yellow-green needles or leaves. Frequently the infestation is diagnosed after the beetles have vacated the tree. For example, when reddish brown foliage is observed the tree is dead and the new generation of bark beetles has already emerged from the tree. Fading foliage throughout the tree crown indicates a dead tree and no insecticide treatment will be effective. Because each bark beetle species attacks only certain tree species, spray only healthy trees that are susceptible to the beetle species attacking nearby trees (for example, pine bark beetles do not attack oaks and oak bark beetles do not attack pines) (Table 1). Insecticide sprays are not recommended against shothole borer and cedar or cypress bark beetles.

How to Apply Insecticides

Insecticide products available to home users are not effective for bark beetle control. Most home gardeners also lack the high-pressure spray equipment and experience to effectively treat large trees. Protective spraying for bark beetles must be done by a licensed pesticide applicator. When hiring a professional applicator, discuss the specific pesticide to be used and effective timing of the application. Also see Pest Notes: Hiring a Pest Control Company. The applicator must use a product with bark beetles listed on the label, and mix and apply the formulation following label directions. Proper application involves thoroughly drenching the main trunk, exposed root collar near the base of the tree, and larger branches (for engraver beetles) with a pyrethroid, such as Astro or Dragnet, or any of the flowable (EC) formulations of the chemical carbaryl to prevent new bark beetle infestations. (Note: These products are not available to home users.) The material must be applied before the new adults penetrate the bark surface of the tree. Regardless of the insecticide used, the applicator should mix only what is needed and dispose of any excess insecticide by properly following label directions.

When to Apply Insecticides

Preventive treatments must be applied to the tree trunk or branches to kill adults before they penetrate the bark and lay eggs. Treatment following successful attacks and egg laying will not be effective. In most cases, the time to apply is in late winter to early spring in warm areas of the state and late spring in cooler and higher elevation areas. For most insecticide treatments associated with bark beetles listed on the insecticide label, generally only one application per year is necessary to provide season-long control. However, depending on local conditions, the life cycle of the beetle, and the insecticide used, in a few situations a second application may be needed several months later to protect individual trees. For example, in California a single spray applied for red turpentine beetle and engraver beetles around mid-February, before adults arrive on new trees, should provide enough control for the home gardener or arborist to implement cultural practices to improve the vigor and defense of pines. However, if strong spring rains or regular irrigation sprinkling of the stem remove the insecticidal barrier, a second application may be necessary.

Red Turpentine Beetle

This beetle is very common on Monterey pines planted in urban landscapes and highway corridors within about 100 miles of the California coast. It is also prevalent on most pines that grow in the Sierra Nevada, particularly on pines damaged by wildfire. Otherwise healthy pines often survive attacks by a few individuals of the red turpentine beetle. Prominent pitch tubes on the lower trunk of standing trees or stumps of recently cut trees nearly always indicate the beetle&rsquos presence. A red turpentine beetle attack likely indicates that pines are stressed from an unfavorable growing environment, injuries, inappropriate cultural care, or that pines are declining from old age. Ensure that planted trees receive proper care and a good growing environment to enhance tree survival.

Western Pine Beetle

This native species attacks the trunk of ponderosa and Coulter pines and creates long winding galleries in the phloem. The trunk quickly becomes covered with small pitch tubes as the beetles can be attracted in large numbers (aggregate) in only a few days. Drought-stressed trees are highly susceptible to attacks by these bark beetles. Heavily attacked trees invariably die and should be removed as soon as attacks are observed. Unattacked trees that are particularly vulnerable, such as during drought or those adjacent to attacked trees, can be protected by watering, if possible, and by applying an insecticide to the outer bark surface before beetles have attacked the tree.

Elm Bark Beetles

Elm bark beetles are pests because they feed in the phloem of elms and spread the fungus that causes Dutch elm disease. The fungus kills the vascular system of elms, causing foliage to turn yellow and brown and then die. Be sure to distinguish diseased trees from those damaged by leaf-chewing caused by elm leaf beetles (Xanthogaleruca luteola). Chewed leaves turn brown, which, when viewed from a distance, resemble discolored leaves caused by Dutch elm disease. If planting elms, choose from among the many new elm cultivars that are resistant to both disease and leaf beetles, as discussed in Pest Notes: Elm Leaf Beetle.


Donaldson, S. G. and S. J. Seybold. 1998. Thinning and Sanitation: Tools for the Management of Bark Beetles in the Lake Tahoe Basin. Reno: University of Nevada Cooperative Extension Fact Sheet FS-98-42 (PDF) .

Dreistadt, S. H., J. K. Clark, and M. L. Flint. 2004. Pests of Landscape Trees and Shrubs: An Integrated Pest Management Guide. Oakland: Univ. Calif. Agric. Nat. Res. Publ. 3359.

Dreistadt, S. H., D. L. Dahlsten, and A. B. Lawson. 2004. Pest Notes: Elm Leaf Beetle. Oakland: Univ. Calif. Nat. Res. Publ. 7403.

Dreistadt, S. H. and E. J. Perry. 2004. Pest Notes: Clearwing Moths. Oakland: Univ. Calif. Nat. Res. Publ. 7477.

Flint, M. L., ed. 2004. Pest Notes: Carpenter Bees. Oakland: Univ. Calif. Nat. Res. Publ. 7417.

Lewis, V. 2000. Pest Notes: Wood-Boring Beetles in Homes. Oakland: Univ. Calif. Nat. Res. Publ. 7418.

Lewis, V. 2001. Pest Notes: Termites. Oakland: Univ. Calif. Nat. Res. Publ. 7415.

Lee, J. C., R. A. Haack, J. F. Negrón, J. J. Witcosky, and S. J. Seybold. 2007. Invasive Bark Beetles. Newtown Square, PA: USDA Forest Service, Forest Insect and Disease Leaflet 176 (PDF) . or at the alternate address.

Marer, P. J., and M. Grimes. 1995. Forest and Right-of-Way Pest Control. Oakland: Univ. Calif. Agric. Nat. Res. Publ. 3336.

Mussen, E. C. 2000. Pest Notes: Wood Wasps and Horntails. Oakland: Univ. Calif. Nat. Res. Publ. 7407.

Paine, T. D., J. G. Millar, and S. H. Dreistadt. 2000. Pest Notes: Eucalyptus Longhorned Borers. Oakland: Univ. Calif. Nat. Res. Publ. 7425.

Rust, M., and J. Klotz. 2000. Pest Notes: Carpenter Ants. Oakland: Univ. Calif. Nat. Res. Publ. 7416.

Sanborn, S. R. 1996. Controlling Bark Beetles in Wood Residue and Firewood. Sacramento: California Department of Forestry and Fire Protection, Tree Notes 3.

Wilen, C. A., D. L. Haver, M. L. Flint, P. M. Geisel, and C. L. Unruh. 2006. Pest Notes: Hiring a Pest Control Company. Oakland: Univ. Calif. Nat. Res. Publ. 74125.


Pest Notes: Bark Beetles

Authors: S. J. Seybold, Pacific Southwest Research Station, USDA Forest Service T. D. Paine, Entomology, UC Riverside and S. H. Dreistadt, UC Statewide IPM Program

Produced by UC Statewide IPM Program, University of California, Davis, CA 95616

Produced by University of California Statewide IPM Program

PDF: To display a PDF document, you may need to use a PDF reader.

Statewide IPM Program, Agriculture and Natural Resources, University of California
All contents copyright © 2019 The Regents of the University of California. All rights reserved.

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Beetle Identification / able to retract its head - Biology

Xyleborus affinis is one of the most widespread and common ambrosia beetles in the world. It is also very common in Florida. Due to its natural attraction to freshly dead wood, the species can be a structural pest of moist timber before the wood is treated. It is also commonly assumed to be the source of tree death because of its abundance in dead or dying trees, but confirmed records of Xyleborus affinis attacking healthy trees are rare. Even in the cases where damage on healthy trees is reported, it is quite likely that the trees have been under some prior unapparent stress, such as recent excess of water.

Like other ambrosia beetles, Xyleborus affinis bores tunnels (called galleries) into the xylem of weakened, cut or injured trees where a symbiotic fungus is farmed for food. Females lay eggs in the fungus-lined galleries and larvae feed exclusively on the fungi.

Figure 1. Adult female Xyleborus affinis. Photograph by Jiri Hulcr, Entomology and Nematology Department and School of Forest Resources and Conservation, University of Florida.

The gardens of Xyleborus affinis usually contain multiple fungus species (Kostovcik et al. 2015). Recent studies have shown that Xyleborus affinis can vector the fungus responsible for laurel wilt disease, Raffaelea lauricola T.C. Harr., Fraedrich & Aghayeva. Laurel wilt is a lethal disease of numerous species of trees in the Lauraceae family (Harrington and Fraedrich 2010, Harrington et al. 2010, Carrillo et al. 2013). In a study conducted by Carrillo et al. (2013), Xyleborus affinis carrying Raffaelea lauricola was shown to attack both redbay and avocado trees, but only transmitted laurel wilt to redbay. Because of this, Xyleborus affinis may become a more serious pest where pathogenic ambrosia fungi are a concern.

Distribution (Back to Top)

Xyleborus affinis is native to the tropical and subtropical regions of the Americas, including Florida (Rabaglia et al. 2006, Atkinson 2014), and has recently spread to most tropical and subtropical regions in the world. Like many other wood borers, Xyleborus affinis can be easily spread through the distribution of wood in international commerce. Although it is among the most widespread and common ambrosia beetles in forested areas around the world, it is often under-reported because it is only weakly attracted to ethanol, the most commonly used lure for ambrosia beetle monitoring (Steininger et al. 2015).

In the US, Xyleborus affinisis is distributed from the east coast of the United States, from Michigan in the north, south to Florida and as far west as Texas. It is also native to South and Central America, including the Antilles, Belize, Costa Rica, El Salvador, Guatemala, Honduras, Mexico, Nicaragua, Panama, and Argentina. The beetle was introduced into Africa, Asia, Australia, Europe and the Pacific Islands including Hawaii (Wood 1982, Rabaglia et al. 2006).

Figure 2: Current distribution of Xyleborus affinis in the New World as of November 2014. The species is also distributed around the world in all warm and humid regions, but that is not shown on this map. Source: Atkinson (2014).

Description (Back to Top)

Adults: This yellowish to reddish-brown species is similar in appearance to other ambrosia beetles in the genus Xyleborus. Most Xyleborus beetles have an elongated, cylindrical body and are yellow, red or light brown in color. Adults of all Xyleborus species are sexually dimorphic, with females being larger than males. Xyleborus affinis females average 2.0-2.7 mm and males are 1.7-2.0 mm in length (Wood 1962, Bright 1968). Males are wingless, have smaller eyes and antennae, and occur in much smaller numbers. The female:male sex ratio has been reported as 8.5:1 in one study (Roeper et al. 1980), but it varies significantly.

This species is very similar to two common Xyleborus species in Florida, Xyleborus perforans Wollaston and Xyleborus volvulus Fabricius. The only reliable way to distinguish Xyleborus affinis from these two is the abdominal declivity, the broad, downward slope at the end of the elytra. In Xyleborus affinis, the surface of the declivity is dull and opaque, in the other two species it is glossy and smooth. More information on identification of Florida&rsquos ambrosia beetles can be found here:

Figure 3: The opaque end of elytra in Xyleborus affinis Eichhoff. Note that the rest of elytral surface is glossy and smooth. Photograph by Jiri Hulcr, Entomology and Nematology Department and School of Forest Resources and Conservation, University of Florida.

Eggs: The off-white, oblong, glossy eggs range in length from 0.6 to 1.0 mm, averaging 0.718 mm. Eggs are laid in groups of two to four along the horizontal tunnels branching away from the main vertical tunnels. In temperatures of 29°C, females have been shown to lay eggs as soon as three days after introduction into the host and up to 27 days (Roeper et al. 1980). One female can lay several dozen eggs, but the number of eggs (and hence larvae) in an individual gallery can be greater because daughters often lay eggs there as well.

Larvae: Larvae are white, legless, and slightly curved. Larvae hatch in 7-14 days at 29°C and in 14-35 days at 22-24°C. They feed exclusively on the farmed fungal symbiont that lines the galleries. There are three larval instars (Roeper et al. 1980).

Pupae: The initially white pupae turn light brown just before adult emergence and average 2.0 and 2.7 mm in length for male and female pupae, respectively. Larvae pupate for 11-23 days at 29°C and 21-35 days at 22-24° C. Adults emerge in 18-35 days at 29°C and 27-35 days at 22-24°C (Roeper et al. 1980).

Biology and Ecology (Back to Top)

Xyleborus affinis is naturally found in moist, fallen logs on the ground of natural forests and rarely interferes with human activities. In large trees, the beetles colonize dead phloem first, followed by the xylem, where the majority of eggs are laid (Jiri Hulcr, unpublished data). The females inoculate the interior of the tunnels they create with the fungal symbiont, which is stored in a specialized pouch called the mycangium inside the beetle&rsquos mouth. Larvae feed on the fruiting bodies of the fungi until adulthood (Carrillo et al. 2013).

As in all other ambrosia beetles in the tribe Xyleborini, Xyleborus affinis is haplo-diploid and inbred. This means that females hatch from fertilized eggs with both the mother&rsquos and the father&rsquos genetic information. Males, on the other hand, only inherit their mother&rsquos genes - they never have a father. Males never leave the original host tree, and their only role in life is to fertilize the females around them, typically their sisters. Females, upon reaching adulthood, either keep reproducing in the same log if conditions permit, or fly out in search of a new host if their native log is too deteriorated (Wood 1982). The ability of Xyleborus affinis to maintain overlapping populations in the same log is unusual among ambrosia beetles because in most species each generation seeks a new host.

Figure 4. Fallen log with frass and bore holes of Xyleborus affinis at Lumber River State Park, North Carolina, July 2010. Photograph by Jiri Hulcr, Entomology and Nematology Department and School of Forest Resources and Conservation, University of Florida.

Xyleborus affinis can live in mutualistic symbiosis with several fungal species, typically in the genus Raffaelea (Kostovcik et al., 2015). As the symbiotic fungus community is diverse and not very specific, the beetle is able to acquire other fungal symbionts from other ambrosia beetles. An example is the recent acquisition of Raffaelea lauricola, a non-native pathogenic ambrosia fungus with which Xyleborus affinis did not coevolve (Carrillo et al., 2013).

Figure 5. Mycangia (=fungus pockets) of the ambrosia beetle Xyleborus affinis in a cross-section of the beetle head. Photograph by Jiri Hulcr and Kyle Miller.

Figure 6. Xyleborus affinis tunnels under bark - an unusual habit for ambrosia beetles, but common in this species. The tunnels contain adults and larvae. Photograph taken in Peru by Jiri Hulcr, Entomology and Nematology Department and School of Forest Resources and Conservation, University of Florida.


Xyleborus affinis is extremely polyphagous and has a known host range of 248 species, angiosperms as well as gymnosperms (Schedl 1962, Wood 1982).

While Xyleborus affinis is a generalist in terms of host tree, it is very selective in terms of host decay status and moisture: it preferentially colonizes larger and very moist pieces of wood that died recently. This species can reach especially high abundance in logs partially submerged in water or lying on moist ground. This is presumably to meet the moisture requirement of the symbiotic fungus.


The presence of Xyleborus affinis can hasten the decline of weak and injured trees, but normally does not cause it. Reports of this species attacking apparently healthy sugarcane and Lauraceae trees exist (Merkl and Tusnadi 1992, Granda Giro 2003, Wood 1982, Carrillo et al. 2013), but as with many ambrosia beetle damage reports, the actual health status of the trees had not been assessed.

Even though this is not an aggressive ambrosia beetle, it has recently become important from the phytosanitary perspective. This is due to the capacity of this species to vector pathogenic ambrosia fungi such as the causal agent of laurel wilt. Thus the spread of Xyleborus affinis from areas infected by this fungus may result in the transport of the pathogen to yet-uninfested regions.

Xyleborus affinis can cause structural damage to timber that is freshly cut (green timber) and has not been dried or chemically treated. Tunneling systems are found throughout the sapwood of the tree, but rarely in the heartwood. Depending on moisture conditions, trees could have numerous superficial tunnels that can be viewed upon pulling back the bark and many tunnels inside the xylem that become apparent when the wood is cut. Xyleborus affinis can cause greater timber damage than some other ambrosia beetles because of its family organization and labor division. While in most ambrosia beetles the gallery is excavated solely by the mother beetle, in Xyleborus affinis the daughter females help expand the tunnel system.

Management (Back to Top)

Typically no active management of Xyleborus affinis is necessary, as the beetle attacks dying or dead trees. However, it can be considered a pest in two circumstances: 1) as a secondary vector of Raffaelea lauricola in avocado groves, and 2) as a structural pest in green wood (non-treated, non-dried, broadleaf species), which is a rather rare event.

Good sanitation and immediate removal of trees showing signs and symptoms of laurel wilt and the use of dried wood for structural purposes is recommended.

Selected References (Back to Top)

  • Atkinson T. (2014). Bark beetles of North and Central America. (1 December 2014).
  • Bright D E Jr. 1968. Review of the tribe Xyleborini in America north of Mexico (Coleoptera:
    Scolytidae). The Canadian Entomologist 100: 1288-1321.
  • Carrillo D, Duncan RE, Ploetz JN, Campbell AF, Ploetz RC, Pena JE. 2013. Lateral transfer of a phytopathogenic symbiont among native and exotic ambrosia beetles. Plant Pathology 63: 54-62.
  • Granda Giro C. 2003. Xyleborus affinis (Eichh) (Coleoptera: Scolytidae) atacando plantaciones de cana de azucar en la provincia de Santiago de Cuba. Fitosanidad 7: 61.
  • Harrington TC, Fraedrich SW. 2010. Quantification of propagules of the laurel wilt fungus and other mycangial fungi from the redbay ambrosia beetle, Xyleborus glabratus. Phytopathology 100: 1118-1123.
  • Harrington TC, Aghayeva DN, Fraedrich SW. 2010. New combinations in Raffaelea, Ambrosiella, and Hyalorhinocladiela, and four new species from the redbay ambrosia beetle, Xyleborus glabratus. Mycotaxon 111: 337-361.
  • Kostovcik M, Bateman C, Kolarik M, Stelinski L, Jordal B, Hulcr J. 2015. The ambrosia symbiosis is specific in some species and promiscuous in others: Evidence from community pyrosequencing. The ISME Journal 9: 126-138.
  • Merkl O, Tusnadi CK. 1992. First introduction of Xyleborus affinis (Coleoptera: Scolytidae), a pest of Dracaena fragrans Massangeana, to Hungary. Folia Entomologica Hungarica 52: 67-72.
  • Rabaglia RJ, Dole SA, Cognato AL. 2006. Review of American Xyleborina (Coleoptera: Curculionidae: Scolytinae) occurring north of Mexico, with an illustrated key. Annals of the Entomological Society of America 99: 1034-1056.
  • Roeper RA, Treeful LM, O'Brien KM, Foote RA, Bunce MA. 1980. Life history of the ambrosia beetle Xyleborus affinis (Coleoptera: Scolytidae) from in-vitro culture. Great Lakes Entomologist 13: 141-145.
  • Schedl KE. 1962. Scolytidae and Platypodidae Afrikas. Revista de Entomologia de Moçambique 5: 1-1352.
  • Steininger MS, Hulcr J, Šigut M, Lucky A. 2015. Simple and efficient trap for bark and ambrosia beetles (Coleoptera: Curculionidae) to facilitate invasive species monitoring and citizen involvement. Journal of Economic Entomology 1-9: DOI: 10.1093/jee/tov014
  • Wood SL. 1982. The bark and ambrosia beetles of North and Central America (Coleoptera: Scolytidae), a taxonomic monograph. Memoirs of the Great Basin Naturalist 6: 1-1359.

Authors: Lanette Sobel, Doctor of Plant Medicine Program, Andrea Lucky, Entomology and Nematology Department, Jiri Hulcr, Entomology and Nematology Department and School of Forest Resources and Conservation, University of Florida
Photographs: Jiri Hulcr, Entomology and Nematology Department and School of Forest Resources and Conservation, Kyle Miller.
Web Design: Don Wasik, Jane Medley
Publication Number: EENY-627
Publication Date: June 2015. Reviewed January 2018.

An Equal Opportunity Institution
Featured Creatures Editor and Coordinator: Dr. Elena Rhodes, University of Florida


Dung beetles are not a single taxonomic group dung feeding is found in a number of families of beetles, so the behaviour cannot be assumed to have evolved only once.

    (order), beetles
      (superfamily), scarabs (most families in the group do not use dung)
        (family), "earth-boring dung beetles" [6] (family), "scarab beetles" (not all species use dung)
          (subfamily), "true dung beetles" [7] (subfamily), "small dung beetles" (not all species use dung) [8]

        Dung beetles live in many habitats, including desert, grasslands and savannas, [9] farmlands, and native and planted forests. [10] They are highly influenced by the environmental context, [2] and do not prefer extremely cold or dry weather. They are found on all continents except Antarctica. They eat the dung of herbivores and omnivores, and prefer that produced by the latter. [11] Many of them also feed on mushrooms and decaying leaves and fruits. One type living in Central America, Deltochilum valgum, is a carnivore preying upon millipedes. Dung beetles do not necessarily have to eat or drink anything else, because the dung provides all the necessary nutrients. [ citation needed ]

        Most dung beetles search for dung using their sensitive sense of smell. Some smaller species simply attach themselves to the dung-providers to wait for the dung. After capturing the dung, a dung beetle rolls it, following a straight line despite all obstacles. Sometimes, dung beetles try to steal the dung ball from another beetle, so the dung beetles have to move rapidly away from a dung pile once they have rolled their ball to prevent it from being stolen. Dung beetles can roll up to 10 times their weight. Male Onthophagus taurus beetles can pull 1,141 times their own body weight: the equivalent of an average person pulling six double-decker buses full of people. [12]

        A species of dung beetle (the African Scarabaeus zambesianus) navigates by polarization patterns in moonlight, [13] the first animal known to do so. [14] [15] [16] [17] Dung beetles can also navigate when only the Milky Way or clusters of bright stars are visible, [18] making them the only insects known to orient themselves by the Milky Way. [19] [18] The eyes of dung beetles are superposition compound eyes typical of many scarabaeid beetles [20] [21] The sequence of images shows a sequence of the beetle rolling a dung ball. It does this to navigate.

        The beetle climbs onto the ball

        The beetle starts to turn around

        The beetle continues turning around

        The beetle rolls the ball with its hind legs

        An earth-boring dung beetle working

        A dung beetle with two balls of dung

        Two dung beetles fighting over a ball of dung

        Cambefort and Hanski (1991) classified dung beetles into three functional types based on their feeding and nesting strategies such as – Rollers, Tunnelers and Dwellers. The "rollers" roll and bury a dung ball either for food storage or for making a brooding ball. In the latter case, two beetles, one male and one female, stay around the dung ball during the rolling process. Usually it is the male that rolls the ball, while the female hitch-hikes or simply follows behind. In some cases, the male and the female roll together. When a spot with soft soil is found, they stop and bury the ball, then mate underground. After the mating, one or both of them prepares the brooding ball. When the ball is finished, the female lays eggs inside it, a form of mass provisioning.

        Some species do not leave after this stage, but remain to safeguard their offspring. The dung beetle goes through a complete metamorphosis. The larvae live in brood balls made with dung prepared by their parents. During the larval stage, the beetle feeds on the dung surrounding it.

        The behavior of the beetles was poorly understood until the studies of Jean Henri Fabre in the late 19th century. For example, Fabre corrected the myth that a dung beetle would seek aid from other dung beetles when confronted by obstacles. By observation and experiment, he found the seeming helpers were in fact awaiting an opportunity to steal the roller's food source. [22]

        They are widely used in ecological research as a good bioindicator group to examine the impacts of climate disturbances, such as extreme droughts [23] and associated fires, [24] and human activities on tropical biodiversity [25] [26] and ecosystem functioning, [27] such as seed dispersal, soil bioturbation and nutrient cycling. [28]

        Dung beetles play a role in agriculture and tropical forests. By burying and consuming dung, they improve nutrient recycling and soil structure. [29] [30] Dung beetles have been further shown to improve soil conditions and plant growth on rehabilitated coal mines in South Africa. [31] They are also important for the dispersal of seeds present in animals' dung, [32] influencing seed burial and seedling recruitment in tropical forests. [33] They can protect livestock, such as cattle, by removing the dung which, if left, could provide habitat for pests such as flies. Therefore, many countries have introduced the creatures for the benefit of animal husbandry. The American Institute of Biological Sciences reports that dung beetles save the United States cattle industry an estimated US$380 million annually through burying above-ground livestock feces. [34]

        In Australia, the Commonwealth Scientific and Industrial Research Organisation (CSIRO) commissioned the Australian Dung Beetle Project (1965–1985) which, led by George Bornemissza, sought to introduce species of dung beetles from South Africa and Europe. The successful introduction of 23 species was made, most notably Digitonthophagus gazella and Euoniticellus intermedius, which has resulted in improvement of the quality and fertility of Australian cattle pastures, along with a reduction in the population of pestilent Australian bush flies by around 90%. [35] [36]

        An application has been made by Landcare Research to import up to 11 species of dung beetle into New Zealand. [37] As well as improving pasture soils the Dung Beetle Release Strategy Group say that it would result in a reduction in emissions of nitrous oxide (a greenhouse gas) from agriculture. [38] There is, however, strong opposition from some at the University of Auckland, and a few others, based on the risks of the dung beetles acting as vectors of disease. [39] [40] There are public health researchers at the University of Auckland who agree with the current EPA risk assessment [41] and indeed there are several Landcare programmes in Australia that involve schoolchildren collecting dung beetles. [42]

        The African dung beetle (D. gazella) was introduced in several locations in North and South America and has been spreading its distribution to other regions by natural dispersal and accidental transportation, and is now probably naturalized in most countries between México and Argentina. The exotic species might be useful for controlling diseases of livestock in commercial areas, and might displace native species in modified landscapes however, data is not conclusive about its effect on native species in natural environments and further monitoring is required. [43]

        Like many other insects, (dried) dung beetle, called qiāngláng (蜣蜋) in Chinese, is used in Chinese herbal medicine. It is recorded in the "Insect section" (蟲部) of the Compendium of Materia Medica, where it is recommended for the cure of 10 diseases. [ citation needed ]

        In Isan, Northeastern Thailand, the local people famously eat many different kinds of insects, including the dung beetle. There is an Isan song กุดจี่หายไปใหน "Where Did the Dung Beetle Go", which relates the replacement of water buffalo with the "metal" buffalo, which does not provide the dung needed for the dung beetle and has led to the increasing rarity of the dung beetle in the agricultural region. [ citation needed ]

        The Mediterranean dung beetle (Bubas bison) has been used in conjunction with biochar stock fodder to reduce emissions of nitrous oxide and carbon dioxide, which are both greenhouse gases. The beetles work the biochar-enriched dung into the soil without the use of machines. [44]

        Several species of the dung beetle, most notably the species Scarabaeus sacer (often referred to as the sacred scarab), enjoyed a sacred status among the ancient Egyptians.

        Egyptian hieroglyphic script uses the image of the beetle to represent a triliteral phonetic that Egyptologists transliterate as xpr or ḫpr and translate as "to come into being", "to become" or "to transform". The derivative term xprw or ḫpr(w) is variously translated as "form", "transformation", "happening", "mode of being" or "what has come into being", depending on the context. It may have existential, fictional, or ontologic significance. The scarab was linked to Khepri ("he who has come into being"), the god of the rising sun. The ancients believed that the dung beetle was only male-sexed, and reproduced by depositing semen into a dung ball. The supposed self-creation of the beetle resembles that of Khepri, who creates himself out of nothing. Moreover, the dung ball rolled by a dung beetle resembles the sun. Plutarch wrote:

        The race of beetles has no female, but all the males eject their sperm into a round pellet of material which they roll up by pushing it from the opposite side, just as the sun seems to turn the heavens in the direction opposite to its own course, which is from west to east. [45]

        The ancient Egyptians believed that Khepri renewed the sun every day before rolling it above the horizon, then carried it through the other world after sunset, only to renew it, again, the next day. Some New Kingdom royal tombs exhibit a threefold image of the sun god, with the beetle as symbol of the morning sun. The astronomical ceiling in the tomb of Ramses VI portrays the nightly "death" and "rebirth" of the sun as being swallowed by Nut, goddess of the sky, and re-emerging from her womb as Khepri.

        The image of the scarab, conveying ideas of transformation, renewal, and resurrection, is ubiquitous in ancient Egyptian religious and funerary art.

        Excavations of ancient Egyptian sites have yielded images of the scarab in bone, ivory, stone, Egyptian faience, and precious metals, dating from the Sixth Dynasty and up to the period of Roman rule. They are generally small, bored to allow stringing on a necklace, and the base bears a brief inscription or cartouche. Some have been used as seals. Pharaohs sometimes commissioned the manufacture of larger images with lengthy inscriptions, such as the commemorative scarab of Queen Tiye. Massive sculptures of scarabs can be seen at Luxor Temple, at the Serapeum in Alexandria (see Serapis) and elsewhere in Egypt.

        The scarab was of prime significance in the funerary cult of ancient Egypt. Scarabs, generally, though not always, were cut from green stone, and placed on the chest of the deceased. Perhaps the most famous example of such "heart scarabs" is the yellow-green pectoral scarab found among the entombed provisions of Tutankhamen. It was carved from a large piece of Libyan desert glass. The purpose of the "heart scarab" was to ensure that the heart would not bear witness against the deceased at judgement in the Afterlife. Other possibilities are suggested by the "transformation spells" of the Coffin Texts, which affirm that the soul of the deceased may transform (xpr) into a human being, a god, or a bird and reappear in the world of the living.

        One scholar comments on other traits of the scarab connected with the theme of death and rebirth:

        It may not have gone unnoticed that the pupa, whose wings and legs are encased at this stage of development, is very mummy-like. It has even been pointed out that the egg-bearing ball of dung is created in an underground chamber which is reached by a vertical shaft and horizontal passage curiously reminiscent of Old Kingdom mastaba tombs." [46]

        In contrast to funerary contexts, some of ancient Egypt's neighbors adopted the scarab motif for seals of varying types. The best-known of these being Judean LMLK seals (8 of 21 designs contained scarab beetles), which were used exclusively to stamp impressions on storage jars during the reign of Hezekiah.

        The scarab remains an item of popular interest thanks to modern fascination with the art and beliefs of ancient Egypt. Scarab beads in semiprecious stones or glazed ceramics can be purchased at most bead shops, while at Luxor Temple a massive ancient scarab has been roped off to discourage visitors from rubbing the base of the statue "for luck".

        Some dung beetles are used as food in South East Asia and a variety of dung beetle species have been used therapeutically (and are still being used in traditionally living societies) in potions and folk medicines to treat a number of illnesses and disorders. [47]

        In literature Edit

        In Aesop's fable "The Eagle and the Beetle", the eagle kills a hare that has asked for sanctuary with a beetle. The beetle then takes revenge by twice destroying the eagle's eggs. The eagle, in despair, flies up to Olympus and places her latest eggs in Zeus's lap, beseeching the god to protect them. When the beetle finds out what the eagle has done, it stuffs itself with dung, goes straight up to Zeus and flies right into his face. Zeus is startled at the sight of the unpleasant creature, jumping to his feet so that the eggs are broken. Learning of the origin of their feud, Zeus attempts to mediate and, when his efforts to mediate fail, he changes the breeding season of the eagle to a time when the beetles are not above ground.

        Aristophanes alluded to Aesop's fable several times in his plays. In Peace, the hero rides up to Olympus to free the goddess Peace from her prison. His steed is an enormous dung beetle which has been fed so much dung that it has grown to monstrous size.

        Hans Christian Andersen's "The Dung Beetle" tells the story of a dung beetle who lives in the stable of the king's horses in an imaginary kingdom. When he demands golden shoes like those the king's horse wears and is refused, he flies away and has a series of adventures, which are often precipitated by his feeling of superiority to other animals. He finally returns to the stable having decided (against all logic) that it is for him that the king's horse wears golden shoes. [48]

        In Franz Kafka's The Metamorphosis, the transformed character of Gregor Samsa is called an "old dung beetle" (alter Mistkäfer) by a charwoman.

        Dragonfly Biology

        Like all insects, the dragonfly is made up of three main body parts: head, thorax and abdomen. The head is a tough, rounded capsule, hollowed out at the back to allow efficient attachment of the neck and to increase head mobility. The mouth is a complex hodgepodge of structures that you would not want to encounter in a dark alley. The upper lip, or labrum, is often considered part of the face. The lower lip, the labium (sometimes called the chin), is made up of three lobes. The labrum and labium function together to capture and secure prey while the jaws do the chewing. The jaws, which work from side to side, are made up of one pair of upper mandibles and two pairs of lower maxillae. These jaws, a series of incurved meat hooks, are worth a close inspection and should be approached with caution in larger species. Species such as dragonhunters and larger darners can drawn blood when they bite.

        The face is a conglomeration of plates separated by seams called sutures. The sutures are often darkened into stripes. The upper half of the face is the frons, and the upper surface of the frons is a shelf-like protuberance on which various diagnostic markings may be found. The compound eye is composed of nearly 30,000 lenses, which work in consort to provide a rich visual image to the dragonfly. They are sight-based creatures who, with a quick turn of the head, are able to scan 360 degrees as well as above and below. Their vision probably allows them to discern individual wing beats, which to us would appear as a blur. They can see ultraviolet and polarized light. Many species also see well in dim light.

        Their two short bristly antennae are thought to function as windsocks or anemometers, measuring wind direction and speed, thereby giving them a method with which to assess their flight. By the way, dragonflies have no sense of hearing, only a rudimentary ability to smell and are unable to vocalize.


        The thorax is the center for locomotion. It is a muscular powerhouse, controlling head, wing and leg movements. Dragonflies are unusual in their wing movements. Most insects’ wings are attached to plates of the chitonous exoskeleton that are, in turn, attached to muscles that move the plates that move the wings. Dragonfly wings, on the other hand, are directly connected to large muscles within the thorax. The interior of the thoracic exoskeleton is massively braced and strengthened to withstand the pressures of these large flight muscles. This bracing can be seen through the exoskeletons of lightly-pigmented individuals such as the Wandering Glider, the Four-spotted Skimmer and the Common Green Darner.

        Thoracic stripes are present in many species. In order to easily communicate the positions of these stripes, the thorax can be separated into three sections: top, shoulder and sides. The top stripes of the thorax will be found in the region between the head and the wings and are best viewed from the front of the dragonfly. The side stripes of the thorax are found below the hindwing attachment point and back toward the abdomen. The shoulder stripes are found below the forewing attachment point, in between the top stripes and the side stripes. Back to the top


        The anatomy of wings and their venation can be very complicated, and one could make a life’s work of just studying them. Most dragonflies can be identified to the level of genus and many to the level of species by just knowing the wing venation. The veins in the wings of dragonflies start as flattened tubes in the compact, tightly folded wings hidden inside the skin of the aquatic nymph. During transformation to adulthood, the veins fill with hemolymph, or insect blood, causing the wings to unfurl. Most of the hemolymph is drawn back into the body after the wings have been fully expanded. The empty tubes and the membranes dry, leaving crisp, tough wings.

        The most obvious feature of a clear, unpatterned wing is the stigma, located on the leading edge of each wing out towards the wingtips. It is thought that the stigma may be used for signaling mates or rivals and may also act as a tiny weight that dampens wing vibrations. The nodus, located at the shallow notch midway down the leading edge of each wing, is an intersection of several large veins and is a point of both strength and flexibility. Because of the structure of the venation around the nodus, the wing is allowed to bend downward (during an upward stroke of the wing) but not upward (during a downward stroke of the wing), resulting in a powerful flight stroke without losing much energy on the return stroke. The wing triangles are located about twenty percent of the way from the wing base toward the tip. The relative size and orientation of these triangles on a dragonfly’s wings can be a clue as to the dragonfly’s family. Originating from an inner, rear corner of the hindwing triangle, the anal loop reaches down into the expanded base of the hindwing. The degree to which the anal loop is present varies from one family to the next. Back to the top


        The abdomen always has ten segments. Segments 1 and 2 appear to be integrated into the thorax and are sometimes difficult to tell from the thorax. To find a particular segment, it is usually best to start with segment 10, far out at the tip, and count backwards. Because of its segmented nature, the abdomen is very flexible and is able to arch up or down (but not side to side). Learn to count abdomen segments as many of our descriptions are based on them.The male abdomen is often narrower (“waisted”) at segment 3, whereas the female abdomen is almost always more robust. Back to the top

        Reproductive System

        The male testes are located in segment 9. Due to the unique nature of dragonfly copulation, the male must transfer sperm to his secondary genitalia, called the hamulus, located in the underside of the second and third segments. The hamulus is a complicated set of “surgical tools” that the male uses for removing the reproductive “investment” made by other males during previous matings. Other parts of the hamulus are then used by the male to fertilize the female with his own sperm. The terminal abdominal appendages of the male are called claspers. The claspers are formed by a pair of upper appendages, called cerci, and a single lower appendage, an epiproct. In some species, the males possess auricles on the sides of segment 2 whose function is to help direct the female’s genitalia to a proper fit with the male’s secondary genitalia during copulation.

        The female terminal appendages consist of a pair of cerci, which have little or no function. In some species, namely the Shadow Darner, they are very brittle and tend to break off. Underneath segment 8 there is either an ovipositor or a subgenital plate, depending upon the species. Both structures are for laying eggs and extend over segment 9 and possibly beyond. Back to the top


        There are several factors you should consider before starting control measures for wood-boring beetles. The first is that no control may be necessary. Many homes have some damage from wood-boring beetles. However, in many cases the damage is very minor and old, which means that all the beetles have died. Unless you see beetles or fresh wood powder around the holes, chemical treatment is not necessary. Fresh wood powder is usually light in color and does not clump. Old wood powder is often yellowed and clumps together.

        Also, there are many beetles in nature that attack wood but do not cause serious damage or reinfest lumber in homes. It is important to know which beetles you have before you go to the trouble and expense of some of the treatments.

        Finally, with the advent of central air conditioning and heating, the potential for widespread damage has decreased. In fact, even with the more serious lyctid and anobiid beetles, if a house has no moisture problems, has a central cooling and heating system, and is not unoccupied for long periods, serious problems are not likely.

        Damage caused by bronze birch borer and twolined chestnut borer

        Trees under stress are more susceptible to attacks by these beetles. Stressed trees are less able to get and move water and food (carbohydrates) to the canopy. This leads to a reduced ability to defend against borer larvae.

        Stress factors

        • Sustained drought.
        • Prolonged defoliation.
        • Poor planting sites, such as compacted soils birch grown in open locations where roots are exposed to heat and drying.
        • Physical damage to roots and trunks from construction damage or lawn mower injury.
        • Construction practices, such as re-grading the landscape.

        Adult beetles feeding on the leaves of trees do not affect tree health. But larvae create destructive galleries under the bark that disrupt the transport of water and nutrients.

        Identifying infested trees is challenging

        • Wilting or yellowing of leaves and dieback starting at the top of the tree.
          • There can be other problems that can cause similar symptoms in the canopy so dieback is not automatically due to borers.
          • Bronze birch borer galleries create raised ridges in the thin bark due to calluses forming over the galleries.
          • Twolined chestnut borer galleries can only be seen when the bark is removed.

          Symptoms of borer damage

          How to protect your trees

          Bronze birch borer

          Native birch species are more resistant to borer attack as long as they are not stressed by drought, over mature or have some other health issue.

          Resistant native species include:

          • White barked birch
            • Paper birch (B. papyrifera)
            • Gray birch (B. populifolia)
            • Yellow birch (B. alleghaniensis)
            • Sweet birch (B. lenta)
            • River birch (B. nigra) seem to be immune

            Most Asian and European varieties of white barked birch are very susceptible to attack even when they are healthy.

            Avoid planting highly susceptible white barked birch species such as:

            • European birch (Betula pendula)
            • Asian birch (B. platyphylla)
            • Himalayan birch (B. utilis)
            • Japanese monarch birch (B. maximowicziana)

            Twolined chestnut borer

            Twolined chestnut borer attacks native and introduced oaks.

            All North American oaks have some resistance, but can suffer damage when trees are stressed.

            Keep trees healthy, minimize stress

            Trees that are stressed, from drought, defoliation or other causes, are more susceptible to damage.

            To minimize stress:

            • Add organic mulch to oaks and birch to improve their health.
              • Mulch keeps soil temperatures cooler and slows the rate of moisture evaporation.
              • It increases the water holding capacity of the soil and creates a better rooting system.
              • Mulch is helpful for birch which has a shallower root system.
              • Root damage caused by soil compaction or root severing due to heavy equipment will stress trees.
              • Remember that the roots can extend well beyond the canopy of the tree.

              Treating trees with pesticides to kill borers is only effective if the tree is in the initial stages of decline and dieback.

              Pesticides are not effective when more than 40 to 50 percent of the canopy has been killed by borers.

              Systemic pesticides

              • Imidacloprid is applied as a liquid drench to the soil around the trunk of the tree (professional applicators can also apply it as a soil injection or a trunk injection).
              • Dinotefuron is applied as granules to the soil directly around the tree (professional applicators can also apply it as a bark spray, soil drench or soil injection).

              CAUTION: Apply these products to birch and oak trees only after flowering in the spring to reduce pesticide exposure to bees. Do not apply systemic pesticides to the soil when bee attractive flowers are planted next to trees.

              Canopy sprays

              Non-systemic control of borers is difficult because precise timing and coverage is necessary. Pesticide is effective if applied to the infested tree when the adult beetles are first active in early June.

              Spray pesticide on the trunk and branches where the eggs are being laid. When the larvae hatch from the eggs, they will come in contact with the pesticide as they burrow through the bark.

              Products containing permethrin, lambda cyhalothrin, and other pyrethroids are effective.

              • Two applications are necessary.
              • The first application should be applied as black locust trees bloom and the second two to three weeks later.
              • Homeowners can spray small trees themselves.
              • Contact professional tree care companies for treatment of larger trees.

              Professional services

              Contact a professional when you are dealing with larger trees. Commercial tree care companies have experience in managing borers and in handling and applying pesticides. They have access to products and procedures that are unavailable to homeowners.

              Watch the video: Carrion beetles Identification (September 2022).


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