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Cannibalizing behaviour in ants

Cannibalizing behaviour in ants


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Today I saw an ant question biology and was reminded of a picture I had clicked 2 years ago.

Here, you can see these black guys cannibalizing this other black guy.

To reiterate, these guys had their nest inside a tree. I had cornered one of them.

If I remember correctly the ant was walking fine and the only fault might have been that I lead the guy astray a bit (not further than the farthest guy in the colony) and near the colony I turned it on its back which lead to a lot of difficulty for getting up again (as any ant knows). I mean I waited maybe a few minutes but it just kept waving it's legs in the air.

So later on as soon as these other ants got sight of their lost friend when it was able to hobble back near the nest, they came over and just pulled him apart.

In the picture you can see the first guy just got to him and the others started aggregating as soon as this guy came over. Within five minutes some 10 or 15 ants were all over the place.

Which ant species is this?

Why did they murder/cannibalize a member of their own colony?

Is this a common behaviour among ants?


Scientific name: Camponotus compressus

Common name: Common Indian black ant

Camponotus compressus tending soft scale insects growing on a stem

Source:

  1. Common Indian black ant
  2. Wikipedia

Cannibalism is common in social insects. It is a way through which they control the population of the colony and conserve nutrients. Members of Hymenotpera (this ant being one) are very quick to consume injured eggs, larvae and pupae. It has been experimentally observed that when a colony of Zootermopsis angusticollis(a species of termite) was kept on a diet full of cellulose i.e. deprived of protein, they attacked their own kind. But cannibalism dropped to zero when casein was introduced in their diet. So it is safe to assume that these ants too engage in cannibalism for the same reason, proteins.

Reference: This book.


Biology of Pseudacteon Decapitating Flies (Diptera: Phoridae) That Parasitize Ants of the Solenopsis saevissima Complex (Hymenoptera: Formicidae) in South America

Pseudacteon flies (Diptera: Phoridae) parasitize individual ant workers, causing decapitation of the host during pupariation. Phorid flies that attack South American fire ants in the Solenopsis saevissima (Smith) complex are distributed across a wide range of habitats and climates associated with the geographical range of their hosts. Sympatric species sharing the same hosts often partition niche resources by season, active time of day, host size, and/or different host activities. They have the potential of being used for biological control of the imported fire ants in North America, Australia, and Asia.

Keywords: Solenopsis invicta natural enemies parasitoid phorid red imported fire ant social insect.

Conflict of interest statement

The authors declare no conflict of interest.

Figures

Decaptating phorid flies with specialized…

Decaptating phorid flies with specialized ovipositors and their parasitic life cycle. ( A…


A great way to come up with science experiments on ants is to start out by watching what they do. Before you collect some from their nest to put in an ant farm, watch how they behave outside. Is there anything puzzling about their behavior that makes you really curious, and makes you want to ask a question, or maybe a hundred questions? Aha! A question is a great way to get started with a science experiment!

We have been watching ants for a long time, and have come up with a few questions of our own, too. We have also come up with some (but not all!) possible answers to our questions and some experiments that you can do to find out if our possible answers seem right. But we don’t know how the experiment will turn out, so it’s up to you to make a prediction about the experiment and then go and find out what happens.

1. How Do Ants “Talk” to Each Other?

If you watch ants for a while, you will notice that they interact with each other a lot. But how are they “talking” to each other? Just as humans have different senses like sight, hearing, touch, and smell, ants could have several different senses, too, which they use to communicate.

Here are some ways you could check to see which senses ants use the most. Try each one out, and make observations about how the ants react.

Sight: Wave something small, like the end of a pencil, close to the ants.
Hearing: Clap your hands.
Touch: Tap the ground close to the ants.
Smell: Blow very gently on the ants.

2. What Do Ants Like to Eat?

Have you ever discovered ants in your kitchen and wondered what they are doing there? Maybe they’re hungry and looking for something to eat! But what kinds of foods do ants like to eat? We came up with the idea that ants like to eat sweet things because they contain sugar, which is a form of energy.

Here are three kinds of sweet things the ants might like to eat: Skittles candies, Life Savers, and honey. If you give all three things to some ants, which one would you predict that the most ants will visit? What else might ants like to eat?

3. How Do Ants Build Their Nest?

If you have ants in an ant farm, you will have a chance to see something really neat: ants at work, digging a nest! But just like there could be a lot of different ways to draw a picture, there could also be a lot of different ways to dig an ant nest!

For example, what shape will it be? Will it be one giant hole, or a lot of small tunnels? Will the ants dig straight down, or will they dig sideways first? Will all of the ants dig at the same time, or will they take turns?

A neat way to answer some of these questions is by using time-lapse photography. What this means is to take a series of photographs of something over time. When you look at all of the photographs together, one after another, you will be able to see how the nest changes over time. You could almost think of a movie as a type of time-lapse photography, where the time between each picture is incredibly short!

For the best time-lapse photography, find a place where you can arrange the nest and the camera in the exact same place to take one picture every day. If you take one picture every day for one week, you should be able to start to see how the ants have been digging their nest!


Odorous House Ants

The odorous house ant, Tapinoma sessile (Say), is considered a pest when it enters structures searching for food, water or nest sites. It cannot sting because it lacks a sting and will likely only bite if you stick a hand into its nest and vigorously disturb the colony. Occasionally winged reproductives found at lights concern residents too. Odorous house ant is common throughout the United States and is the second most common pest ant managed by professionals.

Distribution

Odorous house ant is a small native ant species found in the United States, southern Canada and Mexico. It survives in a variety of environments found from near sea level to elevations of more than 2 miles and can be found in all the continental states. It’s possible that odorous house ant is really four similar-looking species, but until more data are produced to support this hypothesis, we’ll consider it as one. In 2009, it was discovered on the island of Maui, Hawaii and is now characterized as an invasive species.

Identification

Odorous house ant is about 1/8-inch long, dark brown to black and smells like rotten coconut with a hint of other odors when crushed. Its waist is one segmented and lacks an obvious node or bump which easily distinguishes it from other small dark ants, including the Argentine ant. The gaster or abdomen overhangs the waist making the waist difficult to see. Odorous house ant lacks a sting or acidopore (circular ring of hairs) at the end of the gaster, but instead has a slit-like opening on the ventral side of the gaster one segment in from the tip. All odorous house ant workers are the same size or monomorphic.

Behavior and Biology

In addition to their smell, odorous house ants are accurately named as they are often found foraging along the outside base of a home. Increased indoor activity is often associated with rain. Odorous house ant activity can be observed during the day and night and will be found foraging outdoors in greatest numbers when temperatures are between 70 and 86 degrees F. Odorous house ants use edges, ridges or other guidelines to move from one place to another. Natural (vines, trees and shrubs) and man-made (siding, ground/foundation wall interface, wires, pipes, conduits, baseboards, counters and others) objects may serve as guidelines. Outdoors, OHA feed on dead and living insects, dead animals (including those deposited by the family cat), pet food, plant nectar and liquid excrement (honeydew) from aphids, scales and other sucking insects. Indoors, they feed on sweets and other human and pet foods. Odorous house ants are often found foraging to water sources and kitchen and bathroom garbage cans.

Odorous house ants do not build nests within mounds of soil, rather they nest opportunistically. Outdoors, odorous house ant nests in pre-existing spaces that provide some moisture and protection from the sun. They may nest under, near or in logs, landscape timbers, stones, patios, leaves, debris, siding including that laid on the ground, stacked wood or firewood, mulch, pine straw, bee hives, dog houses and near iris rhizomes. Indoors, they may be associated with food or moisture and can be found beneath edges of carpets and toilets, in cabinets or drawers, near or under garbage cans and other similar places. Indoor nests are often associated with outdoor nests. Often many nests are present outdoors and a few may be found inside.

Odorous house ants have many queens per colony (polygyne) but queen number varies. In natural situations, such as forests, colonies tend be small with one queen (monogyne). However, in disturbed, urban environments, many queens and tens of thousands or more workers may be present in a colony that has many nests. Workers are more dominant when present in larger numbers (urban environments) than smaller numbers (forests).

Because indoor odorous house ants are often in contact with outdoor odorous house ants, management efforts during the warmer times of the year can often be directed to the outside to impact the indoor ants.

Steps to manage odorous house ants include:

  1. Correctly identify the ant. See above for identification details.
  2. Remove conducive conditions that allow odorous house ant to thrive. Determine the food, water and harborage that the home and near landscape (within 10 ft) provide to the ants and then move/remove as many as possible.
  3. Monitor and inspect to locate nests and areas of activity. To help locate odorous house ant nests and activity, place index cards with a smear of honey every 10 – 20 ft around the base of the structure. Check the cards in 40 minutes and count the number of odorous house ants. Follow the ants back to their nests and note nest location.
  4. Bait areas of activity. Bait outdoors where more than 10 odorous house ants are found per index card. Baiting indoors where ants are active as a sole treatment will most likely provide a short-term reduction in indoor ant foraging.
  5. Treat nests. Because many nests can be found around a structure, it is difficult to locate all of them. Treating nest sites as the sole treatment method would be most effective when just a few small nests are present. Finding nests sites often involves lifting objects to expose the nest. Inspect and treat nests at the same time to avoid disturbing the ants and causing them to move prior to treatment.
  6. Treat perimeter, entry ways and areas of activity. A typical perimeter treatment involves spraying the ground/foundation wall interface, the siding/foundation wall interface and the area around doors, windows and vents. Recent changes to pesticide labels have restricted the areas where perimeter sprays can be applied. Read labels carefully to avoid misapplying the pesticide and possibly causing unintended run-off. Treat areas of ant activity if allowed by label. Both slow-acting and fast-acting perimeter treatments can dramatically reduce the number of outdoor foraging odorous house ants, but may slowly affect indoor ant activity if baits have not been used.Applying fast-acting crack and crevice sprays or dusts to ants indoors will have little effect on outdoor odorous house ant populations and may prolong indoor activity. Avoid applying fast-acting insecticides to interior cracks and crevices as the sole treatment.
  7. Combine above. Integrated pest management relies on multiple tactics and managing odorous house ant is no exception. The best management results will be achieved with a combination of the above practices. Correctly identifying the pest ant and correcting conducive conditions should always be used when managing odorous house ant infestations. Monitoring and inspecting to note nest location and activity is especially helpful. Combining different chemical treatments (e.g., slow-acting insecticide applied to the outside perimeter with an exterior bait placed where ants are active) should increase pest management success.

Check with your local Extension service for product recommendations as pesticide registrations differ in each state.

Video

Don’t let tramp ants take over your home, an All Bugs Good and Bad eXtension Webinar

Excerpted from Vail, K. and J. Chandler. 2018. Odorous House Ants: The Most Common House-invading Ant in Tennessee. UT Extension https://extension.tennessee.edu/publications/Documents/W473.pdf

Sources

Buczkowski, G. and G.W. Bennett. 2006. Dispersed central-place foraging in the polydomous odorous house ant, Tapinoma sessile as revealed by a protein marker. Ins. Soc. 53:282–290.

Buczkowski, G. and G.W., Bennett. 2008. Seasonal polydomy in a polygynous supercolony of the odorous house ant, Tapinoma sessile. Ecol Entomol 33:780–788.

Buczkowski, G. 2010. Extreme life history plasticity and the evolution of invasive characteristics in a native ant. Biol Invasions 1387-3547.


Far from powerless: Ant larvae cannibalize eggs, are influenced by relatedness and sex

A larva of the ant species Formica truncorum cannibalizes an egg by piercing its shell and consuming the contents. Credit: Nick Bos

To the casual observer, the colonies of social insects like bees and ants appear to be harmonious societies where individuals work together for the common good. But appearances can be deceiving.

In fact, individuals within nests compete over crucial determinants of fitness such as reproductive dominance and production of male eggs. The intensity of competition often depends on the level of kinship between colony members. This is because selfish individuals lose indirect fitness when their behavior harms close relatives. A new study by Eva Schultner and colleagues from the Universities of Helsinki, St. Andrews and Oxford reveals that in ants, such social conflict occurs even among the youngest colony members: the eggs and developing larvae.

In behavioral experiments conducted at Tvärminne Zoological Station in Finland, ant larvae acted selfishly by cannibalizing eggs, but levels of cannibalism were lower when relatedness among brood was high. In addition, male larvae engaged in cannibalism more often than female larvae.

Using evolutionary modeling, the researchers show that cannibalism is predicted to evolve when it carries a benefit to the cannibal (for example in the form of increased survival), and that the costs of consuming kin influence the intensity of cannibalism behavior. Differences in cannibalism benefits for male and female larvae on the other hand may be responsible for higher levels of cannibalism in males.

By exploring the evolutionary causes and consequences of selfish larvae behavior, the study published in The American Naturalist sheds new light on the evolutionary constraints of competition in social insect colonies, and demonstrates how in complex societies, even the youngest individuals are potential players in social conflict.


Far from powerless: Ant larvae cannibalize eggs, are influenced by relatedness, sex

To the casual observer, the colonies of social insects like bees and ants appear to be harmonious societies where individuals work together for the common good. But appearances can be deceiving.

In fact, individuals within nests compete over crucial determinants of fitness such as reproductive dominance and production of male eggs. The intensity of competition often depends on the level of kinship between colony members. This is because selfish individuals lose indirect fitness when their behavior harms close relatives. A new study by Eva Schultner and colleagues from the Universities of Helsinki, St. Andrews and Oxford reveals that in ants, such social conflict occurs even among the youngest colony members: the eggs and developing larvae.

In behavioral experiments conducted at Tvärminne Zoological Station in Finland, ant larvae acted selfishly by cannibalizing eggs, but levels of cannibalism were lower when relatedness among brood was high. In addition, male larvae engaged in cannibalism more often than female larvae.

Using evolutionary modeling, the researchers show that cannibalism is predicted to evolve when it carries a benefit to the cannibal (for example in the form of increased survival), and that the costs of consuming kin influence the intensity of cannibalism behavior. Differences in cannibalism benefits for male and female larvae on the other hand may be responsible for higher levels of cannibalism in males.


Contents

The binomial name Tapinoma sessile was assigned by Thomas Say in 1836. Sessile translates to "sitting" which probably refers to the gaster sitting directly on top of the petiole in the abdomen of the species. [8] The common names "odorous house ant" and "coconut ant" come from the odor the ants produce when crushed, which is very similar to the pungent odor of a rotting coconut, blue cheese, or turpentine. [1]

The gaster portion of the abdomen sits directly on top of the petiole in the abdomen of this species, which helps distinguish them from other small, dark, invasive ants. [8] A comparison of the side view of T. sessile (below) and a diagram of the a typical ant body (below) shows how T. sessile’s gaster sits atop its petiole. This leads to a very small petiole and to the gaster being pointed downward. The anal pore then opens ventrally (toward the abdomen) instead of distally. [8] Their antennae have 12 segments. [6]

A side view of the body of T. sessile. It shows that the gaster part of the abdomen is directly above the ant's petiole.

A diagram showing the names of the different sections of a typical ant's body. Note that the petiole in this "typical ant" is in front of the gaster, rather than under it.

The antennae of T. sessile has 12 distinct segments

The queens lay the eggs which incubate between 11–26 days. After hatching, the larval stage lasts between 13–29 days, and the pre-pupal and pupal stages last between 10–24 days. [6] Little is known about the lifespan of the ant, though it has been shown that queens live at least 8 months (and probably much longer), workers at least a few months (and show every indication of living as long as queens), while males appear to live only approximately a week. [ citation needed ]

T. sessile is native to North America and ranges from southern Canada to northern Mexico, but is less common in the desert southwest. [6]

Colonies vary in size from a few hundred to tens of thousands of individuals. Big colonies usually have multiple queens. [6]

The odorous house ant is tough: Injured workers have been observed to continue living and working with little hindrance, some queens with crushed abdomens still lay eggs, and there are documented instances of T. sessile queens surviving without food or water for over two months. They also appear highly tolerant to heat and cold. These ants are difficult to remove from a home after their colony has become well-established. [5]

When offered a choice of food sources, the ants preferred sugar and protein over lipids, and this preference persisted in all seasons. When specific sugar sources were studied the ants preferred sucrose over other sugars, such as fructose or glucose. [3]

Food allocation Edit

Foragers collect food that is around the nest area and bring it back to the colony to share with the other ants. T. sessile has polydomous colonies, meaning that one colony has multiple nests. Because of this, T. sessile is very good at foraging for food when there is great variance in the distribution of resources. Instead of going back to a faraway nest to deliver food, they move workers, queens, and the brood to be closer to the food, so that they can reduce the cost in effort of food transport. This is called 'dispersed central-place foraging'. [2] It was also found that the half-life of the stay at any one nest was about 12.9 days. [10]

Buczkowski and Bennett also studied the pattern of food movement within a nest. They labeled sucrose with Immunoglobin G (IgG) proteins, and then identified them using an enzyme-linked immunosorbent assay (ELISA) to track the movement of food. They found that food was spread through trophallaxis (one animal regurgitating food for another). Despite this trophallactic spread of food, the workers kept most of the sucrose. They also found that some queens received more food than others, suggesting a dominance hierarchy even between queens. They also found that the nests were located in a system of trails, and that their distribution depended on where food was found and the distance between these patches of food. [2] It was also found that the rate of trophallactic feeding depends on the number of ants per nest, and the quality of food available. When the number of donors is kept constant, but the number of total individuals in increased, more individuals test positive for the food marker. This indicates that more individuals are eating, but the amount they eat is less. If the number of donors was doubled, and the size of the overall population increased, the number of individuals receiving food more than doubled, again indicating that the number of individuals fed increased, but that the per capita amount of food consumed decreased. [11]

When searching for food, primary orientation is when ants are exploring a new terrain without the guidance of odor trails. Secondary orientation is when terrain has been explored, and there are pre-existing odor trails which ants use to orient themselves. When T. sessile ants are orienting themselves for the first time they often rely on topography. The major types of elements they rely on are bilaterally elevated, bilaterally depressed, unilaterally elevated, and unilaterally depressed. They use these types of surfaces to orient along, and lay the first odor trails, which can then be followed in the future, to the food source, by other ants. [12]

Seasonal behaviors Edit

It was also found that this ant species practices seasonal polydomy (having multiple colony sites) to have access to multiple food sources. The colony will overwinter in a single nest, and then during spring and summer when resources are more abundant they will form multiple nests. This allows them to better use food sources, that might be spread out. During the winter they will return again to the same nest location. Seasonal polydomy is rather rare, and only found in 10% of all polydomous species. [13] Seasonal polydomy is not found in many ant species, but there are many ant species, including T. sessile, which move within a season: Migration to better forage sites is common. [10]

Seasonal activity patterns of the ants were also studied, and corresponding to the seasonal polydomy, it was observed that the ants displayed the most activity between March and September and displayed almost no activity from October to December. Daily activity patterns were also studied. In March T. sessile foraged during the day, but in April that pattern changed and the ant began to forage during both day and night. During most of the summer, T. sessile shows low levels of activity throughout the day and night. [14]

Competition with other ants Edit

Competition between species is often classified as exploitation or interference. Exploitation involves finding and using limited resources before they can be used by other species, while interference is the act of preventing others from getting resources by more direct force or aggression. When it comes to these behaviors, a species is considered dominant if it initiates an attack and subordinate if it avoids other species. In comparison with eight other ant species, T. sessile was more subordinate on the dominant to subordinate scale. The ant does not show a large propensity for attack, preferring to use chemical secretions instead of biting. [4]

When T. sessile, a subordinate species, was in the presence of dominant ant species such as C. ferrugineus, P. imparis, Lasius alienus, and F. subsericea, they reduced the amount of time spent foraging. This was tested with the use of bait, and when the subordinate species, such as T. sessile, encountered a dominant species they would leave the bait. It would then make sense that the subordinate species would forage at a different time than dominant species, so that they could avoid confrontation, but there is sizable overlap in foraging period on a daily and seasonal basis. Because T. sissile forages at the same time as dominant species, but avoids other foraging ants, they must have excellent exploitative abilities to survive. [14]

One of the invasive species that T. sessile has had to contend with is the Argentine ant (Linepithema humile). Studies of its interactions with L. humile has helped researchers better understand the aggression of T. sessile. T. sessile ants rarely fight alongside their nest-mates: They only were observed to have fought collectively in six of forty interactions. This often caused T. sessile to lose altercations with other ant species, such as L. humile, even when more T. sessile individuals were present. Whereas other ant species like L. humile fight together, T. sessile do not. T. sessile is, however, more likely to win in one-on-one interactions because they have effective chemical defenses. [15]

Other habits Edit

This species is a scavenger / predator ant that will eat most household foods, especially those that contain sugar, as well as other insects. Indoors they will colonize near heat sources or in insulation. In hot and dry situations, nests have been found in house plants and even in the lids of toilets. Outdoors they tend to colonize under rocks and exposed soil. They appear, however, to form colonies virtually anywhere, in a variety of conditions. [ citation needed ]

In experiments where T. sessile workers were confined in an area without a queen, egg-laying (by the workers) was observed, though the workers destroyed any prepupa that emerged from the eggs. [5]

Odorous house ants have been observed collecting honeydew to feed on from aphids, scale insects, and membracids. [ citation needed ]

They appear to be more likely to invade homes after rain (which washes away the honeydew they collect). [ citation needed ]

Odorous house ants appear to be highly tolerant of other ants, with compound nests consisting of multiple ant species that included T. sessile having been observed. [ citation needed ]

Some birds and toads will eat odorous house ants on occasion. [ citation needed ]

Wheeler (1916) mentions Bothriomyrmex dimmocki as a possible parasite of odorous house ant colonies, suggesting that B. dimmocki queens invade and replace T. sessile queens. [ citation needed ]

Isobrachium myrmecophilum (a small wasp) appears to parasitize odorous house ants. [ citation needed ]

T. sessile are not hard to control they are vulnerable to most ant-killers, which are especially effective when applied as soon as their presence is noticed. If dealt with early, their numbers can be brought under control in just a few days. However, the longer a colony is ignored, the larger the population becomes and the longer it will take to clear the infestation – possibly a few weeks. [5] These ants most commonly invade buildings in late winter and early spring (particularly after rain), at which times one should be on the lookout for newly-arrived ants foraging indoors. [6] [10]

To discourage immigration, standing water should be eliminated in the house, as T. sessile are attracted to moisture. [3] Plants should be trimmed away from buildings, so they do not make convenient routes for above-ground entry. Cracks, holes and joints should be sealed with polyurethane foam or caulk, especially those that are near the ground. Firewood, rocks, and other materials should not be stored next to a home because it provides sites for nest building [1] near the home, and T. sessile naturally relocate their colonies to be near successful forage sites. [6] [13] [2]


RESULTS

Food searches in the open desert terrain and in channels

The main results presented in this study rely on experiments performed in 7 cm-wide channels that connected the ant nest to a feeder or to a test channel without food (Fig. 1). While such channel experiments have frequently been performed in the past (e.g. Cheng and Wehner, 2002 Sommer and Wehner, 2004 Steck et al., 2009 Wittlinger et al., 2006), we wanted to ascertain that the searches in the channels are similar to the searches in the open field, or, if there were quantitative differences, we wanted to be able to assess these. Fig. 2 illustrates that search behaviour in the field and in the channels is indeed similar. To compare searches performed in the two situations, C. fortis foragers were allowed to find a feeder established 10 m from the nest and retrieve a food morsel from a large number of cookie crumbs (>800). Ants reliably search for such a plentiful feeding site on their next foraging trip, which was recorded with the feeder being removed. The searches recorded in the open field (Fig. 2A) are clearly centred on the previous location of the feeder. And when the ants' search trajectories are projected onto the nest-feeder axis, the resulting search distribution (Fig. 2B) is very similar to the search distribution recorded in the channel (Fig. 2C). This concerns both medians and spreads (details in Fig. 2 legend).

Food abundance at the feeding site

Desert ants are apparently able to judge the yield of a feeding site upon their first visit. This is demonstrated by the data in Fig. 3A,D. The search median was centred on the previous nest–feeder distance only if the feeder had been supplied with many food items (>800) (Fig. 3A). If just one, five or 25 food items had been offered, the ants centred their searches farther away from the nest, between 13 and 14 m, and the search spread was larger (details in Fig. 3 legend). The groups with one, five or 25 food items in the feeder differ significantly from the group with a full standard feeder (ANOVA on ranks with Dunn's post hoc test, P<0.01 for one and 25 food items, P<0.05 for five food items against the group with a filled feeder).

The same tendency is discernible for the variances of the individuals' searches (Fig. 3D). Ants that had previously visited a full feeder exhibited consistently small search variances (low variance and low spread of variances), while the searches for the feeders equipped with 1–25 food items were altogether more variable. No significant differences were observed here, however (ANOVA on ranks, P=0.088).

Schematic diagram of the channel setup. Arrangement of training and test channels length of channels is not to scale nest–feeder orientation 180 deg compass direction. For further details, see Materials and methods.

Schematic diagram of the channel setup. Arrangement of training and test channels length of channels is not to scale nest–feeder orientation 180 deg compass direction. For further details, see Materials and methods.

Desert ants' search behaviour in the open field and in channels. For the two-dimensional search density plot (A), the numbers of ants' visits to each 25×25 cm pixel of the feeder surrounds was recorded, summed and normalised to the maximum number of visits per pixel observed in the plot. The darkest red represents the highest density (100%), the darkest blue just a single visit (note individual walking trajectories discernible near the margin), and black areas were not searched at all (0%). Recordings lasted for 2.5 min after the animal had left the nest (red pixel on the left-hand margin) nest–feeder distance was 10 m. The ants (N=31) had visited the full feeder (>800 cookie crumbs) once before the recordings were made. (B) To construct the box plot, the data in A were projected onto the nest–feeder axis i.e. any movements along the axis perpendicular to the nest–feeder direction were disregarded. Turning points were only recognised if the respective animal walked more than 40 cm into the new direction along the nest–feeder axis, in correspondence to the channel recordings (see Materials and methods) only those animals that performed at least 6 turning points according to this criterion were evaluated this reduced the number of ants from 31 in A to 22 in B. (C) The box plot presents searches recorded in the test channel used in all the other experiments described in this report. The ants had visited a full feeder once in the training channel before the recordings were made. Note the similarity of the plots in B and C, attesting to comparable search behaviour in the channel and in the open field on the level of the present analysis. Box plots show medians, spreads (+75th, −25th percentiles) and whiskers (+90th, −10th percentiles).

Desert ants' search behaviour in the open field and in channels. For the two-dimensional search density plot (A), the numbers of ants' visits to each 25×25 cm pixel of the feeder surrounds was recorded, summed and normalised to the maximum number of visits per pixel observed in the plot. The darkest red represents the highest density (100%), the darkest blue just a single visit (note individual walking trajectories discernible near the margin), and black areas were not searched at all (0%). Recordings lasted for 2.5 min after the animal had left the nest (red pixel on the left-hand margin) nest–feeder distance was 10 m. The ants (N=31) had visited the full feeder (>800 cookie crumbs) once before the recordings were made. (B) To construct the box plot, the data in A were projected onto the nest–feeder axis i.e. any movements along the axis perpendicular to the nest–feeder direction were disregarded. Turning points were only recognised if the respective animal walked more than 40 cm into the new direction along the nest–feeder axis, in correspondence to the channel recordings (see Materials and methods) only those animals that performed at least 6 turning points according to this criterion were evaluated this reduced the number of ants from 31 in A to 22 in B. (C) The box plot presents searches recorded in the test channel used in all the other experiments described in this report. The ants had visited a full feeder once in the training channel before the recordings were made. Note the similarity of the plots in B and C, attesting to comparable search behaviour in the channel and in the open field on the level of the present analysis. Box plots show medians, spreads (+75th, −25th percentiles) and whiskers (+90th, −10th percentiles).

From these data, two tendencies are evident. With a large number of food items, (1) the search tended to be centred more accurately on the position where the food had been presented during the first visit, rather than on positions farther away from the nest, and (2) spread and variance decreased, indicating a more focused search.

Experience with the feeding site

The reliability of food available at the feeder appears to focus the search in a similar way to a high abundance of food in the feeder, perhaps even more strongly (Fig. 3B,E). After five or more training visits to the feeder, the ants that had experienced a full feeder and the ants that had encountered just one or five food crumbs showed no significant differences in their search behaviours. The searches were focused on nest–feeder distances of

12 m, i.e. noticeably further from the nest than the original feeder position. Compared to the group with just one training run, the search medians thus shifted, from 9.85 m to 11.85 m in the group with many food crumbs, and from 14.43 m to 12.30 m for the group with five food crumbs. The variances of the searches also decreased significantly [test for variances (after Sachs, 1999) with Holm–Bonferroni correction for multiple comparisons five food crumbs, P<0.01 many food crumbs, P<0.05 for values for percentiles and variances, see Fig. 3 legend]. In the group with one food crumb, no notable shift occurred (12.75 m to 12.78 m) and the changes in variance did not yield significant differences either (even though intra-individual variances decreased, see below).

The most striking features in Fig. 3B and Fig. 3E are the reduced variances of the search distributions in the experienced ants. This is illustrated most clearly in Fig. 3E, with the search variances being similar to the situation with a full feeder visited just once (Fig. 3D, bottom box plot). These reductions were significant for the groups with five and with many food crumbs in terms of variance in search medians (Fig. 3A,B) and for the groups with one food crumb in terms of intra-individual variance (Fig. 3D,E).

Is food density a proxy for food abundance?

Ants do not literally count (e.g. Franks et al., 2006), raising the question of how Cataglyphis assesses food abundance. As an initial enquiry into this question, we changed the density of food items but kept their number constant (Fig. 3C,F). Twenty-five food crumbs were offered in a standard feeder of 32 mm diameter or in a small feeder of 8 mm diameter, thus increasing food density 16-fold. The ants that had paid a single visit to the small feeder exhibited a search pattern that significantly shifted towards the pattern elicited by a full feeder. The search median changed from 14.10 m (large feeder) to 11.60 m (small feeder) (the value for one visit to a full feeder was 9.85 m). This shift of the search medians was statistically significant (t-test, P=0.013) and the variances of the search medians also decreased significantly (P<0.02) (Fig. 3C). Changes in intra-individual variances were not significant, however (Fig. 3F).


Parasite grants ants "eternal youth" – but there's a dark side

Eternal youth is the first thing many of us might wish for if we stumbled onto a genie or a magic monkey’s paw, but there’s always a catch. Now, scientists have discovered a version of this story playing out in ant nests, as parasites drastically extend the lifespan of worker ants – at a terrible cost.

By definition, parasites are bad news for the host, competing for nutrients or other resources. But at first glance, that didn’t seem to be the case for the relationship between Temnothorax nylanderi, ants and Anomotaenia brevis tapeworms. The parasites live in the ants’ guts, where they seem to bestow their hosts with much longer lifespans than uninfected ants.

To investigate what’s going on, researchers at Johannes Gutenberg University Mainz watched 58 colonies of the ants for three years, some infected with the parasites and some without. By the end of that period, none of the original uninfected worker ants were still alive – but about 53 percent of the infected insects were. The upper limit for how long they could live remains unknown, due to the length of the study, but the trend so far seems to put them about on par with queens, which are known to survive for up to 20 years.

Even at their advanced age, the infected ants still retained their youthful bodies. Young ants start off a yellow color, usually turning brown as they age and their skin hardens – but infected ants stayed yellow.

And the deal gets even cushier. Infected ants were far less active than usual, never leaving the nest or chipping in to help with any of the usual tasks. Instead, they lazed around the nest while their uninfected colony-mates fed them, groomed them and even carried them around. In some cases, they were attracting more attention than the queen herself.

A closeup of the head of a Temnothorax nylanderi ant

And that’s where the dark downside creeps in. It seems like a pretty sweet gig for the individual infected insects, but the colonies as a whole began to suffer. Uninfected ants appeared to be more stressed out and were dying younger than they might have if the parasites didn’t show up at all.

There’s also the question of what’s in it for the worms themselves, and the team found that the parasites are playing the long game by keeping the infected ants coddled and lazy. It’s only a matter of time before a woodpecker comes knocking on the nest, and while healthy ants will scatter, the infected ones just sit there and await their fate.

The endgame is that these worms reproduce inside the woodpecker’s gut. The birds poop out the tapeworm eggs, where ant foragers will stumble onto them and feed them to their young in the nest, starting the cycle over anew.

On closer inspection, the team found some metabolic changes in infected ants that drive this biology and behavior. When worker ants are “promoted” to queens, certain genes switch on that boost their lifespan – and the worms also seem to be able to turn these on in their hosts. Infected ants also give off unique chemical signals – the main method of communication between ants – that drive their broodmates to want to look after them.

All up, it’s another fascinating example of the kind of microscale drama and intrigue we might be walking past on a daily basis. Insidious as it is, this story sounds a bit less horrifying than the fungus that turns ants into zombies.

The research was published in the journal Royal Society Open Science.


Foraging behavior of ants: Experiments with two species of myrmecine ants

Experiments presented in this paper for two species of ants confirm the predictions of models based upon the hypothesis that the animals maximize the net rate of energy intake while foraging.

Solenopsis geminata in the laboratory recruited at higher rates to patches of sugar solution when the distance to a patch decreased, the diameter of a patch increased, or the sugar concentration increased.

Pogonomyrmex occidentalis in its natural setting recruited at higher rates to patches of seeds mixed with pebbles when the distance to a patch was decreased, the size of the patch was increased (when recruitment was already at a high level), the density of seeds was increased, or seed size was increased. When presented with a uniform distribution of seed sizes within a patch, this species tended to choose intermediate-sized seeds, but there was no tendency to choose a narrower range of seed sizes as the distance to the patch increased. This last finding was the only one inconsistent with a model based on maximization of net rate of energy intake.

The tendency for Solenopsis to respond to sugar concentration and for Pogonomyrmex to respond to seed size refutes the predictions of models based on minimization of the average time required to obtain each food item.

Increased temperature increases running speed. Thus, when the temperature increased during an experimental session for Pogonomyrmex, a particular rate of recruitment to a patch was maintained by a decrease in the total number of recruits on the trail to the patch.

Further analysis of the Pogonomyrmex results reveals that different levels of response to variable changes in the various experiments can be explained in terms of the model. This indicates that interference among recruits to a patch is always important to the level of response.


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