Results matching “solenopsis invicta”

Ants in an ant hill

How many ants are in one ant hill?


Dear Samir,

Thanks for your question!

Ants are abundant: they collectively rival with humans as dominant organisms on terrestrial ecosystems, weighing as much as all humans present on Earth; and, combined with termites, they comprise almost a third of animal biomass in tropical terrestrial habitats! The reason for such success is their social nature. More, there are around 16,000 described ants species in the world, and we think there is approximately the same number of species yet to be discovered. As their large species number indicates, ant societies exhibit a diverse array of behavior, morphology, and also nest sizes.

While Myrmoteras barbouri has around 8 individuals in their colonies, some species of nomad ants that live in the old world, A.K.A driver ants, may have nests with several million individuals. Another good example of large nests is the ones built by Atta sexdens, a leaf cutter ant living in the Neotropic, which may possess 5 to 8 million ants!

myrmoteras.jpg Full face view of the charismatic Myrmoteras barbouri, whose nest possesses very few ants. This ant species lives in the Indomalaya bioregion. Image by Estella Ortega/

siafu7-L.jpg Dorylus driver ants in Kibale, Uganda. Image by Alex Wild (

Among the diversity of ants we find on Earth, there are the mound-builder ants. Their nests are more than a pile of revolved soil covering an underground home; they have symmetric shape, complex interconnected systems of galleries and chambers, and are often thatched with leaves and stems fragments, or adorned with pebbles. Those types of nest indicate habitats under extreme climate. The mound reduces the loss of temperature and humidity, while it also increases the area exposed to sunlight, keeping the nest warmer than the outside environment. Their thatched or pebble sprinkled roofs are an additional heat source (think of how warm is a stone under the sunlight, or the heat produced by material in decomposition), besides preventing evaporation.

FormicaObscuripesNest-S.jpg Thatched mound nest of Formica obscuripes, an ant found in North America. Image by Alex Wild (

The nests of some mound-building ants, such as Formica (also known as wood ants), often last for many decades, and they can be massive, rising from the soil surface as much as 5 feet (1.5 meters).

A thatched mound nest of Formica rufa, found in Palearctic region, may have 4 million ants; while in North America, nests of the western thatching ant Formica obscuripes, house around 40,000 ants. The soil mound nests of Solenopsis invicta possess approximately 100,000 individuals.

casent0178134_p_1_high.jpg Lateral view of Solenopsis invicta, a tramp species found in the United States. Image by April Nobile/

You will find interesting information on mound nests and thermoregulation here.

All the best,

Flavia Esteves & the AntAsk Team

Can I train ants? (Ryan)

Hello Antblog,

I am interested in conducting some experiments with ants and I had a few questions I'd like to ask before I get started and I thought your site would be a good place to start.

1) Can queens of different varieties be trained(forced) to co-exist in one colony if an abundance source of food is present?

2) What is the smartest breed of ants?

3) Could ants in an ant farm learn to farm aphids? How might I go about doing this?

4) Could ants survive on honey alone?

5) Could ants be trained to use little man made tools for things such as cutting or digging through rock?

6) Can ants smell and identify different metals such as iron, nickel, gold, etc.?

I understand these questions are very vague and I do not expect a direct answer for all of them, but any information is appreciated. I'd even like additional links I could go explore myself.
I am only a grade 12 student but I am very interested in ants. My ultimate goal is to create a super ant farm to test the capabilities of ants as well as teach them to advance as a species.

Hi Ryan,

I apologize in advance: this post is probably too long and too speculative. The answers to a few of your questions are simple: (6) I don't think so; (4) some ants can; (3) it's thought that this is not a learned behavior, but some ants do facultatively tend aphids; (1) no, unless they are social parasites (for more stuff on social parasites, click here, here, and here).

Questions #2 and #5 are pretty complicated, philosophically and biologically, so I'm going to spend most of the rest of this post talking about them.

But real quick, before I dive into a heady diatribe about the philosophy of psychometry: ants and honey:

Could ants survive on honey alone? Adult ants don't need very many nutrients, and can survive for at least a week or two (often more) on just sugar water or diluted honey. It is the egg-laying ability of the queen, and the growth of the larva that depends on more protein-rich food sources, like (depending on the ants) seeds or insects. Several groups of ants seem to have bacteria living in their guts that can help them make nitrogen (one of the important building blocks of life that we need to synthesize proteins), but I'm not sure if anyone has quantified how only raising these ants on carbohydrates influences how many eggs the queen can lay, and how fast the larvae can grow. For many ants, we don't know their exact dietary requirements, but by and large, the ants that are most likely to be able to get by on a sugar-water or honey-only diet are arboreal (spend most of their time in trees). Carpenter ants (genus Camponotus) and Acrobat ants (genus Crematogaster) are among the most likely candidates that you'd run into outside of the tropics. Similarly, with respect to your question (3), many of the same ants that are largely herbivorous will occasionally tend aphids or other related phloem-sucking insects. But I'm not aware of a learning component to this behavior: I think it's hard-wired.

Okay. Onwards and upwards.
You know, when I tell people that I study ants, I am often asked (by males especially) if I am working on weaponizing them or figuring out how to harness them for industry. Ants are, after all, famously industrious. There is even an ancient Greek/Indian/Russian legend about ants that mine gold (sort of). I read about it in the book "Shalimar the Clown" by Salman Rushdie (which is a great novel if you're interested in 20th century geopolitics, but doesn't have much useful information about ants).

In general, the major hurdle to training ants for any specific anthropocentric end is the way in which they actually get things done. Deborah Gordon has a really nice book about ant behavior called "Ant Encounters" that I highly recommend. One of the key aspects of ant behavior she does a really good job explaining (not least because she pioneered this research) is "emergence." Her research, and the research of other people who study social insects, is much of the inspiration towards work in "Swarm intelligence" in robotics and computer science. Basically, the problem-solving ability of the colony, or "intelligence" does not arise from the leadership or intelligence of a few ants, but emerges from the trial and error of many non-intelligent individuals. Thus, to train a swarm, you'd really need to understand how voting works in these true, blind democracies. Here are a few links you can check out if you want to learn more. Deb Gordon and Tom Seeley are some of the most eloquent speakers and important researchers on the biological side of swarm intelligence (read/listen/watch more here, here, and here).

The most compelling examples of humans modifying ant behavior are not the results of training, but of trickery. It's easy to get ants to walk where you want them to walk, think a given nestmate is dead, and become alarmed by isolating one of the pheromones they use to communicate, and applying it in the right way. However, I can't think of a way in which you could use pheromones to trick ants into picking up tools, or finding gold, unless you could splice the gene for pheromone production into a bacteria that preferentially grew and expressed that gene in the presence of that metal. This is not completely implausible, and as we learn more about the genomic architecture of ants, and the metabolic pathways involved in pheromone production, using a genetically-modified bacteria-ant system could potentially become economically viable (and probably less ecologically destructive than most current mining techniques). One could aerially spray genetically-modified bacteria over an area that already has high ant densities, using the bacteria to trick the ants into collecting soil particles with high concentrations of metal oxides. Then, a few months later, when the ants have collected the clumps of soil with the most metal oxides, one could find large ant colonies and spray another strain of genetically-modified bacteria directly into the nests, that would make the "dead ant" pheromone in the presence of high concentrations of the metal oxide. After a few days, one could go around collecting the midden piles at the surface of the nest, which would be enriched in the target metal oxide. This sort of strategy would probably work best in desert or grassland environments, where a few species of ants build conspicuous nest mounds, like Pogonomyrmex in the American Southwest. It's possible one might be able to do this chemically, without genetically modified organisms of some sort, but if there was a much simpler way of using ants to work for us, someone (especially in Greece, Russia, or India) probably would have figured it out.

Beyond pheromonal trickery, it is possible that we'll be able to eventually trick ants electrochemically, as you can "currently" (get it? like, electrical current?) do with cockroaches:
It's possible that, by controlling one ant with electrical impulses, you could convince the rest of the colony to do your bidding. However, as Tom Seeley found with bees, nestmates might need to be convinces themselves of the validity of the scouts choice, in which case you'd need to coordinate quite a few ants to agree that, for example, a vein of gold is a food source. The trickery arguments above apply primarily to ants that often recruit to a food source; however, there are ants that primarily hunt alone.

As you may have figured out by now, your question "which ant is most intelligent?" depends on what kind of intelligence you're talking about. The types of ants most likely to exhibit high degrees of swarm intelligence are the ants that form the biggest colonies, and need to forage collectively. Leaf cutter ants (especially Atta and Acromyrmex) and army ants (especially Eciton and Dorylus) form colonies of hundreds of thousands of individuals in the wild, and many types of invasive ants (such as the Red Imported Fire Ant, Solenopsis invicta) form sprawling super-colonies that can cover acres in their introduced ranges. I'm not aware of a "swarm intelligence" test (but see Seeley's work on, for example, nest-finding abilities of honey bees in Maine), but the number of worker ants involved, the foraging range of the colony, and the complexity of the environment would all likely factor in. It would be interesting to compare how quickly swarms of different sizes and species could solve a maze, for example. I'm not aware of a study like this: perhaps you could set something up!

Observations of ants in the wild can allow one to make at least cursory qualitative statements about swarm intelligence in ants. The complexity and scale of leaf cutter ant nest architecture, the many tasks involved in maintaining a fungal monoculture, and the hazards of foraging in tropical savannas and forests leads me to suggest that the attines may exhibit the highest degrees of emergent, swarm intelligence, perhaps surpassed only by the fungus-growing termites of the African and Australian tropics. A foraging swath of army or driver ants (Eciton or Dorylus) may be collectively be processing millions of environmental signals per second: scent and vibrational cues about proximity of prey and colony members, light ant dark cues, etc., which is similarly impressive.

Basically everything listed in the paragraph about ants here (and the suspiciously similar list here) is a result of "swarm intelligence," and not at all related to the individual intelligence of any of the colony members. Personally, I don't think there is a clear winner between ants and termites in terms of the complexity that emerges from the swarm intelligence of their respective superorganisms. And I'm somewhat tempted to write a whole 'nuthur blog post on what is wrong with these two articles... perhaps some other time.

So far as individual, organism-level intelligence goes: again, I can only speculate. I am tempted to guess that the ants that have small colonies and have large workers that forage by themselves are most likely be more individually intelligent, because colony fitness will depend to a greater extent on the problem-solving ability of ants acting individually, rather than the emergence of intelligence from trial-and-error and blind democracy. Conversely, I would expect very small ants that live in very large colonies to be the least intelligent, individually, because, as a colony, they can rely on swarm intelligence to effect reproduction. In primates, the "social brain hypothesis" (also, see here) suggests that group size should be positively correlated with brain (neocortex) size. An assumption this hypothesis makes is that intelligence is necessary to maintain group cohesion through diplomacy, strategy, and individual recognition. In most social insects, group cohesion is pheromonally-mediated, so intelligence need not scale with group size. However, in some groups of ants and wasps, there is a shifting dominance hierarchy, which might mean individuals have to remember each other and behave according to past experiences. Elizabeth Tibbetts, to the astonishment of the behavioral and entomological communities, demonstrated face recognition in certain wasps with changing social hierarchies that are reinforced by in-fighting, rather than solitary wasps or eusocial wasps with hormonally-mediated social hierarchies. Thus, the ants that are most individually intelligent (e.g., the most train-able) may be ants that have shifting social hierarchies, and/or spend much of their time hunting by themselves. We're still learning more about the social lives of different species of ants: if you include species that haven't been described or discovered, there are probably more than 20,000 ant species in the world, and many of them have remarkably divergent ways of life. Several species I can think of which have to contend with a reality of changing dominance hierarchies (often due to unconventional reproductive strategies) throughout the lifetimes of individual workers, include ants in the genera Pristomyrmex, Platythyrea, Myrmecia, and Cerapachys. Myrmecia include some of the largest and most visually-oriented ants (two factors often correlated with increased brain size). They are also among the largest of ants, and very effective solitary hunters. So I would guess that some member of the genus Myrmecia might be the smartest ant, on an individual basis. Other strong contenders include ants that forage alone and use visual cues to navigate back to their nests, such as Gigantiops destructor, Cataglyphis, and Melophorus.

"Tandem running," a behavior in which one ant basically takes another ant by the hand and leads them to a food source (actually, they just tap each other's antennae pretty much the whole time) has been proposed as the first example of "teaching" in insects (by their definition, the "waggle dance" of bees is simply "broadcasting").
However, a critique of this article by some of the leading non-human intelligence researchers takes issue with this definition of learning, with implications for how intelligence might be defined (not to mention an implicit critique of the education system). Definitely check out the Lars Chittka's publications page for a veritable treasure trove of readings on insect intelligence.

Not to end on too preachy a note, but your statement "help them advance as a species" is problematic on two counts: (1) ants are a family, the Formicidae, which is comprised of more than 14,000 described species, and (2) "advance" has very strong teleological overtones. Teleology is an understandable (Nietzche was all about it, and would have been really happy with you for using that sort of reasoning). But it's not the way I think biology works. Saying you would like to domesticate ants, or modify them behaviorally or biologically so that they are more useful to humans is one thing, but the advancement of a species is an empty concept. Evolution is change, not change towards a goal.

To wrap it all up: swarm intelligence has many advantages at the colony level, but should not be confused with the individual intelligence of organisms. Without broad, cross-species comparisons of either kinds of intelligence, I can only speculate (perhaps beyond the limits of my own intelligence) about which ant is the smartest. Both types of intelligence would require different approaches to training or other types of behavioral manipulation. If there were an easy way to train ants for industry, someone would have probably figured it out by now. Emerging biotechnologies may make the use of ants (and/or ant cyborgs... cy-ants?) possible, but assembling little robots (equipped with both swarm and individual intelligence) from scratch might be prove to be easier, at least in the short run.

Whew! Was that enough to get you started? :)
Jesse Czekanski-Moir & the AntAsk Team

Dear AntAsk,

I was wondering how thermoregulation works in ants?

Thanks in advance!

Dear Farzaneh,

This is actually a great question! We have forwarded your question to Clint Penick (photo of Clint with a large wood ant thatch mount at the end of this post), who has studied thermoregulation in some ant species. Here is his response:

"Ants are ectotherms (or "cold-blooded"), which means that they rely on their environment for thermoregulation. This can be seen in their nest structure. Ants usually construct deep, underground nests that maintain fairly stable temperatures. In the summer, ground temperatures provide shelter from the heat, and in the winter the ground is warmer than the outside air. The winter ant, Prenolepis imparis, builds some of the deepest nests known to ants (close to 12 feet or 3.6 meters below the surface), and these ants retreat to the cool shelter of their nests during the summer and only come to the surface during cooler months.

Many ants build their nests under rocks, which can serve as solar collectors. This is why ant researchers are sometimes called "rock flippers," because many species of ants can be found under rocks, especially in the morning when these rocks begin to heat up. Because rocks often stick above the ground surface, they have a lower specific heat than the surrounding ground. This means that they will heat up faster during the day-even under shady conditions-but they also cool down faster at night.

Some ants have developed special nest structures that aid in thermoregulation. These ants are the "mound builders." The fire ant, Solenopsis invicta, builds a mound out of soil, which is riddled with a spongiform network of tunnels. These mounds serve the same function as rocks-they collect solar thermal energy and have a reduced specific heat so they heat up faster than the ground. Fire ant larvae grow best at 32ºC, so workers move their larvae up to the surface of the mound early in the morning as the mound begins to heat up. By mid day, the surface of the mound is too hot, so the ants move the larvae deeper into the nest to track the optimal temperature. By nightfall, all of the larvae and most of the colony is located deep underground where temperatures are more stable. In fact, this behavior is so reliable it can be used as a natural compass: the ants bring all their larvae to the south side of the nest in the morning, where the sun's rays are the strongest. To see an example of a mound nest of the fire ant, check out this previous post here.

The species that build the largest mounds, however, use a completely different process. These ants, which are called "thatch builders," live in northern Europe and Scandinavia. Thatch mounds can be over two meter tall and are built out of decaying pine needles and leaves. Like a compost pile, the leaves of the mound release heat as they decompose, and this plant material also provides insulation. While fire ant mounds reach their highest temperatures on the outer surface, thatch mounds are warmest near the center of the mound where the heat from decomposition is the strongest. In addition to the mounds, thatch ants also use their own bodies to heat the interior of their nests. Worker ants sun themselves on the surface of the mound and then quickly run inside to heat up the interior of their nest with their warm bodies. To see an example of a thatch nest of a wood ant, check out this previous post here.

Solar collector vs thatch mound.png

Figure courtesy Clint Penick

Other insects, like honey bees, can generate internal body heat by flexing their flight muscles. Ants don't have flight muscles, but their bodies do produce a limited amount of heat. Army ants, like Eciton burchelli, don't dig nests in soil, but instead construct hanging bivouacs out of their own bodies. They are able to use the collective heat of their bodies to keep warm over night, and they can adjust their position to allow ventilation during the day.

Honey bees can also ventilate their nests by using their wings like fans. Again, ants don't have wings, so they use different methods for nest ventilation. The massive colonies of Atta fungus-gardening ants are topped with a dome of soil that has small chimneys. As winds blow over the nest, convection over the chimneys pulls stagnant air out of the nest and allows fresh air to flow back inside. This has a negligible effect of nest temperature, but it does help cycle CO2 out of the nest and increase oxygen levels inside."

Atta nest ventilation.png

Figure courtesy Clint Penick

Clint Penick (guest expert), Steffi Kautz & the AntAsk Team

Formica mound-1.jpg

Guest expert, Clint Penick, with a Formica polyctena thatch mound in northern Estonia

Dear Ant Experts,

I have a large colony of ants in my yard (or possibly many colonies) in Surprise, AZ. These ants are becoming a small problem because they love to bite my family. So far I have tried many "ant baits" and found that they ignore all of them except for amdro pellets which contain Hydramethylnon. Boiling water works great on them when I can locate their hills, but they always return. Any information on what kind of ants these are and how to eradicate them will be very appreciated! Thank you in advance!


Thumbnail image for Thumbnail image for CRW_8103.jpg

Dear JJ,

I wish I had some encouraging news for you, but it's likely you have Solenopsis xyloni, a close relative of the Red Imported Fire Ant, Solenopsis invicta. You're already doing some of the most effective things: Amdro was developed specifically to target S. invicta (or RIFA, as it's sometimes called in the invasive species literature). It works best if you pour about 1/4 cup directly onto the mounds, and re-treat every 2-3 weeks. In general, poisoned baits usually kill at most about 90% of the colony, so re-treatment is essential. Boiling water, as you said, is also great when you can find the colonies. Just don't pour it over the Amdro! It doesn't work when wet!

The problem is, unless you and your family live on a 1,000-acre ranch, miles away from town, surrounded by a moat and a flying-ant-proof fence, you'll always risk re-infestation from the surrounding area. Therefore, the only further advice I have is to get organized with your community. It might make sense to bring this problem up with your neighbors, at your children's schools, and any local organizations you're involved with. The "School of Ants" is a citizen-science project that would be a fantastic way to gather information about where other colonies of these ants occur in your area...and the students might even learn a thing or two about the biology and ecology of ants!

One critical bit of information you can get from collaborating with the folks at "School of Ants," or other experts, is a positive identification of these specimens. Solenopsis invicta and Solenopsis xyloni are difficult to tell apart from pictures, but one is a native ant that can be a nuisance, and one is an invasive ant that costs the USA more six billion dollars a year to control nation-wide. More information on Solenopsis invicta, and some advice about distinguishing it from related species, can be found on this excellent site.
Either way, you have the opportunity to raise awareness in your community about ants, so that you can more effectively solve the problem you have now, and be prepared for future ant invasions.

Good luck!
Jesse Czekanski-Moir & the AntAsk Team

I'm not an ant observer, but I recently noticed ants on my sidewalk behaving in a manner I hadn't seen before.

The sidewalk is shaded by an oak tree that is dropping thousands of tiny, hard cone-like kernels about 1/8" long and slightly less in diameter. Simultaneously this tree also drops mature acorns, so I don't know whether the tiny cones are related to the acorn process or not. The ants are also very small - 1/8" or less long.

About a week ago, I noticed occasional tightly gathered 'circles' of cones - usually about 1-1/2" to 2" in diameter, and about one to three or four cones in height. Upon further examination we discovered the circles were being 'built' by the ants, and also discovered that these 'circles' were being built around dead or dying caterpillars. Some ants were continuing to build the pile - while a steady stream of others were going back and forth - presumably carrying bits of the caterpillar back to the nest. After the ants abandon the pile, there is nothing left of the caterpillar.

I suspect this is not an unusual ant activity, but since I know little about ant behavior, I'm curious about the reason for the temporary burial of the caterpillar. Are they hiding or protecting their food-source from other predators - restricting the movement of a still living caterpillar - or what?

Here are a couple of photos - the first showing the cones as they distribute when they fall, and the second shows a caterpillar in the process of being surrounded and covered.

Thanks for your help.

Dave Owen
Lakeland, FL


Dear Dave,

As you live in Florida, we reached out to a Florida ant expert, Lloyd Davis, and here is what he had to say:

"About this ant behavior: First, the "cones" are caterpillar dung. I suspect from the color of the ants on the caterpillar that the ants are imported fire ants. I have seen fire ants bring dirt onto a glue trap to gain access to food trapped in the glue. This however looks too far fetched. Unless someone watched the process and saw the ants positioning the caterpillar dung, I suspect some other reason for their arrangement and that it is just a coincidence that the ants are feeding on the caterpillar in the middle of the pile."

In the insect world, we often call insect "dung" or waste by the name frass. This may explain why the frass is accumulating near the caterpillar as this is the source.

Red imported fire ants (Solenopsis invicta) are unfortunately common in Florida. You can see photos of them here and here.

To learn more about red imported fire ants you can read some of our previous posts including here and here.

Thank you for contacting AntBlog,
Corrie Moreau & the AntAsk Team


Hi Corrie -

Thank you for pursuing an answer to my 'ant' question and notifying me of Mr. Davis on-line response; however I'm still puzzled by a number of points that likely have been explained had I been more thorough in my question.

If the 'cones' are, as Mr. Davis says, caterpillar frass, I am astounded by the quantity, distribution, size and shape uniformity (they look very much like sub-miniature pine cones or a tiny shelled ear of corn). When I spoke of 'thousands' of the little 'cones', it was not an exaggeration. Although no longer happening, when it was the entire portion of the sidewalk beneath the oak tree (roughly 160 sf) would be littered with these 'cones' within 24 hours after the sidewalk was swept. Incidentally, the appearance of the 'cones' started about two weeks before I wrote, and stopped almost totally and suddenly a few days after my previous note. Except when there was a 'circle', the distribution of the cones was almost uniform over the entire sidewalk area beneath the tree - and oddly there never any on the sidewalk beyond the foliage of the oak tree.

I should have noted that I did personally see the ants constructing these 'circles', and there was always a dead caterpillar or other insect in the middle. It was amusing to see these tiny ants (perhaps 1/16" in length is more accurate than 'smaller than 1/8"') swinging the 'larger-than-themselves' cones to and fro as they carried them to the pile. As the 'cone-circles' grew, the cones around the pile almost totally disappeared, defining an increasingly larger 'empty' circle largely devoid of cones (the 'cleared' circles got as large as 6" in diameter from the pile center).

I'm very familiar with imported 'fire ants', and the 'circle-builders' may well be that type, although they seem smaller and darker in color than the many other colonies we constantly battle on our large lot. These ants are almost black in color - with just a hint of red, and both front and back seem to be rounded - rather than 'wasp-shaped'. The fire ants we have in our yard all have piles of excavated sand around them that continue to grow until we poison them. The small ants about which I wrote seem to live beneath the sidewalk, and I've not seen any excavated dirt or sand, although I know it must be there.

Neither my sister nor I have ever noticed this phenomenon before in the many years we have lived here. If it does happen again, I'll try to get more information and a close-up photo of an ant moving one of the cones.

Again, I want to thank you and Mr. Davis for responding to my inquiry.


Regarding your second inquiry, here is what another ant expert, James Trager, had to say:

"I agree that the "cones" are caterpillar frass, and from their size, would even go as far as to suggest that they were produced by some sort of oak-feeding saturniid. Leaves are not an especially nutritious food, especially tannin-filled oak foliage, so caterpillars have to eat prodigious amounts to fuel their rapid growth rates, from tiny egg to several-inch long caterpillar in just a couple of weeks or so. This explains the rapid appearance and disappearance of the frass, and why all the frass was under the drip-line of the tree. .

Fire ants almost invariably bury large items for butchering. It doesn't surprise me that, in the absence of convenient soil particle, sawdust, or what-have-you, the ants used caterpillar frass for their burying ritual. The smaller, darker description of the ants also fits for a "butchering party" of fire ants. These gatherings usually comprise mostly or only the smaller workers, which are more uniformly dark colored."

I hope this helps!

All the best,
Corrie Moreau, James Trager, & the AntAsk Team

Cocoon or not cocoon? That is the question.

Hi Ant folk:

I am interested in finding out if ants in the Myrmicinae tribe produce silken cocoons as I am trying to get hold of some samples. Do you know anyone who has Acromyrmex echinator, Atta cephalotes, Pogonomyrmex barbatus or Solenopsis invicta in culture who might have some cocoon samples hanging around (if they exist)?

Thanks for your help.
Cheers, Holly


Hello Holly:

No ant in the subfamilies Myrmicinae, Pseudomyrmecinae or Dolichoderinae is known to produced larval silk. The adaptive significance of this fact, and the metabolic fate of their silk production genes and anatomy is not well studied (unknown?), though perhaps one of the others on our team may know more.

Mature larvae of most species in the other subfamilies normally do spin a cocoon before pupating, so those are where you'll have to seek the materials in question, I suppose.

Just wondering, how did you arrive at this particular list of species?

Best regards, James C. Trager of the AskAnt Team.


Hi James,

Very interesting. I came across the list of ants as I have been looking for the silks genes from the genome projects. Our lab has done a bit of work on silks from Formicinae and Myrmeciomorphs in the past and I am looking to add to the dataset.

It's interesting that you say Dolichoderinae also don't produce silk as Argentine ants have also been sequenced. Do Myrmicinae, Pseudomyrmecinae or Dolichoderinae have unique domiciles? Are they weaker than other subfamilies?

Thank you for your response and I look forward to having a few more ant conversations.

Cheers, Holly


Hello Holly:

Myrmicinae and Dolichoderinae are diverse taxonomically and ecologically, with a wide range of nesting habitats, about which no generalizations may be made. Pseudomyrmecinae are almost all inhabitants of cavities in plants, and interestingly, species in the huge genus of Formicinae called Camponotus vary in cocoon production in a way that may be interesting to you. Soil and dead and rotten wood inhabiting ones typically have pupae in cocoons, while many that inhabit the tight confines of plant stems, notably the subgenus Colobopsis, lack cocoons.

Nonetheless, I rather think that lack of cocoons could be more of a nutritional matter than a matter of where particular ants live. A diet dominated by nectar, honeydew and fruit juice, or by seeds, is low in protein, so perhaps it was adaptive for the mainly nectarivorous or granivorous ancestors of these groups to eliminate silk production in order to conserve amino acids for growth and development. Many Formicinae are evidently more carnivorous than at some of the Dolichoderinae and Myrmicinae, and at least some have nitrogen-fixing, internal bacterial symbionts that could mitigate the nitrogen compound deficiency. I hope that my making this sweeping, and perhaps wrong guess/generalization will stimulate commentary from some others, and perhaps other myrmecologists can be brought into the discussion . . .

Do let us know if you hear from them.

Regards, James C. Trager of the AskAnt Team

Vestigial features in ants? (Haley)


I'm doing a biology project about evolution and I was wondering if ants, specifically the common carpenter or fire ant, has any vestigial features, and what may have been their function.


Hi Haley,

This sounds like a very interesting biology project! Vestigial traits are reduced or incompletely developed structures. These features are non-adaptive and have no function, but are clearly similar to functioning organs or structures in closely related species. Vestigial traits are homologous among related species and are evidence for common descent and a shared evolutionary history. In ants, vestigial traits have not been extensively studied and there are just a few examples. Remains of wings in the worker cast, called "gemma" have been described in some ant species: in pupae of the ponerine Diacamma ceylonenese (Baratte et al. 2005), in larvae of the red imported fire ant Solenopsis invicta (Bowsher et al. 2007), and in Pheidole morrisi (Sheibat et al. 2010). Vestigial spermatheca are present in some basal ant lineages (Gobin et al. 2008). These vestigial traits are particularly interesting as the queen caste still possesses functional wings and functional spermatheca, but the workers do not. Workers cannot fly and mate. Some ant lineages are sting-less, but possess vestigial traits of the sting apparatus, for example the entire Formicinae subfamily. This subfamily includes the genus Camponotus (carpenter ants). Other vestigial traits are the absence of functional eyes in army ant species (see photo of Eciton burchellii below). These ants are blind, but show remains of the eyes.

army ant.jpg

Soldier of the army ant Eciton burchellii with vestigial eye structures. Photo by Alex Wild (

Here are the relevant citations:

Baratte S, Cobb M, Deutsch J and Peeters C. 2005. Morphological variations in the pre-imaginal development of the ponerine ant Diacamma ceylonense. Acta Zoologica 86: 25-31.

Bowsher JH, Wray GA, Abouheif E. 2007. Growth and patterning are evolutionarily dissociated in the vestigial wing discs of workers of the red imported fire ant, Solenopsis invicta. Journal of Experimental Zoology (Mol. Dev. Evol.) 308B:769-776.

Gobin B, Fuminori I, Billen J, Peeters C. 2008. Degeneration of sperm reservoir and the loss of mating ability in worker ants. Naturwissenschaften 95:1041-1048.

Shbailat S J, Khila A, and Abouheif E. 2010. Correlations between spatiotemporal changes in gene expression and apoptosis underlie wing polyphenism in the ant Pheidole morrisi. Evolution and Development 12: 580-591.

I hope this helps!
Steffi Kautz & the AntAsk Team

Larval development


I have a question i hope you can answer for me.

I have recently started my own ant colony which is currently thriving. The ants have even created a new nest which is full of larvae at various stages of development.

I may need to provide a bigger habitat for them in future judging by how many larvae there seems to be in the new nest. However im not sure how long it takes the for an ant to go from a new layed larvae to an ant thats ready to go.
Could you give me some idea of the timeline for this?

The ant species i have is Polyrhachis Australis.
Any information you can provide me with would be grately appreciated.

Regards, Michael

Hello Michael:

Congratulations on your thriving Polyrhachis australis colony.

The question of how long it takes an ant to develop from egg to adult has been studied in only a relative few of the 14000 or so known kinds of ants. Most of the ones studied are those which infest buildings or are agricultural pests. Two house infesting ants, the Pharaoh ant Monomorium pharaonis and the ghost ant Tapinoma melanocephalum develop quite quickly, about three weeks from the laying of an egg by the queen to an adult worker, while fire ants Solenopsis invicta take about a month from egg to adult. On the other hand, some Myrmica species from the cold north of Siberia and Canada may take about two years to complete their development.

Unfortunately, your Polyrhachis australis fall into the category of ants whose development has not been studied. But I would estimate, based on my experience with related ants, that they complete their development in 8-12 weeks, in part depending on temperature. In other words, you might want to prepare for the rapid expansion of your colony with additional nesting space, sooner than later.

James C. Trager & the AntAsk Team

Live ants perceived as dead? (Jon)

I heard of a study wherein ants were sprayed with a chemical that dead ants usually gave off and their nest-mates carried them off as if they were still dead even though they were still alive. Have you heard of this study and if so do you know where I can find it?


Hi Jon,

Thanks for your great question! The story is true. Researchers can capture the smell of a dead ant (or any insect) by dipping it in organic solvents (usually hexane) for a couple of minutes. The solvent can then be applied to another object or individual. The ants perceive this experimentally treated object or individual as dead and dispose it to the colony's dump sites. This behavior makes a lot of sense, because a dead and rotting individual would present a threat to the colony as disease could spread easily.

There are some great studies on this behavior (called necrophoresis):

Blum MS (1970) The Chemical Basis of Insect Sociality. In: Beroza M, editor. Chemicals Controlling Insect Behavior. New York: Academic; pp. 61-94.

Choe DW, Millar JG, Rust MK (2009) Chemical signals associated with life inhibit necrophoresis in Argentine ants. PNAS 106:8251-8255.

Gordon DH (1983) Dependence of necrophoric response to oleic acid on social context in the ant, Pogonomyrmex badius. J Chem Ecol. 9:105-111.

Haskins CP, Haskins EF (1974) Notes on necrophoric behavior in the archaic ant Myrmecia vindex (Formicidae: Myrmeciinae) Psyche 81:258-267.

Howard DF, Tschinkel WR (1976) Aspects of necrophoric behavior in the red imported fire ant, Solenopsis invicta. Behaviour 56:157-180.

Visscher PK (1983) The honey bee way of death: Necrophoric behaviour in Apis mellifera colonies. Anim Behav. 31:1070-1076.

Wilson EO, Durlach NI, Roth LM (1958) Chemical releasers of necrophoric behavior in ants. Psyche 65:108-114.

All the best,
Steffi Kautz & the AntAsk Team

Hi Antweb,

I am a PhD student in Synthetic Biology and I've read that you talked about artificial insemination trials in ants, which have not be very successful. Would you mind giving me the references of the papers talking about that?


Hi Xavier,

Thanks for your question! As you have read in this post on "How to breed ants", artificial insemination in ants has not been very successful and only been tested on very few species. Cupp et al. (1973) conducted an experiment in which the authors decapitated males. Queens were anesthetized with CO2, and stroked against the males to induce ejaculation. This experiment was done using fire ants (Solenopsis invicta). Read here to find out more about the red imported fire ant.

In a study by Bell et al. (1983) instrumental insemination was conducted, also using the fire ant Solenopsis invicta. Virgin queens were induced to fly, anesthetized with CO2 and inseminated with either a mixture of sperm extracted from the male seminal vesicles and accessory gland contents or sperm alone. Of the females we artificially inseminated 65% produced workers. Artificial insemination techniques have also been carried out using Atta leaf-cutter ants (den Boer et al. 2010).

A recent review article on the copulation biology of ants has been published by Boris Baer (2011) in the journal Myrmecological News. Here is a link to the pdf. In this paper, some more references to studies conducting artificial insemination in honey bees and bumble bees are given.

All the best,
Steffi Kautz & the AntAsk Team


Ball DE, Mirenda JT, Sorensen AA & Vinson SB (1983) Instrumental insemination of the fire ant, Solenopsis invicta. Entomologia Experimentalis et Applicata 33: 195-202.

Baer, B (2011) The copulation biology of ants (Hymenoptera: Formicidae). Myrmecological News 14: 55-68.

Cupp EW, O'Neal J, Kearney G, Markin GP, (1973) Forced copulation of imported fire ant reproductives. Annals of the Entomological Society of America 66:743-745.

den Boer SPA, Baer B, Boomsma JJ (2010) Seminal fluid mediates ejaculate competition in social insects. Science 327: 1506-1509.

I was just wondering how red imported fire ants behave in colder climates, how far do they go underground and would they come out if I disturbed the nest?

Hi Charlie,

Some information on what ants do in the winter is here. A fair amount of research has been done on fire ant temperature tolerance as a way of predicting the limits of its invasive range. Typically, fire ants will not leave their nests to forage when the soil temperature is below ~15º C (~59º F). At lower temperatures they often go deep underground to protect themselves from the cold. However, this does not mean that they will not become aggressive if the nest is disturbed. When the sun is shining and the temperature is cooler, fire ants move to the part of their mound that is being hit by sunlight to warm up. So even if the temperature is relatively low, they may be present and active in the top of the mound. At much lower temperatures, they are most likely to be inactive in the deeper parts of the colony and probably will not come out even if the nest is disturbed. In the lab, fire ant mortality is high if kept at freezing or near freezing temperatures for several days. However, colonies of fire ants in the wild have adaptations for dealing with the cold and can live in places where the minimum temperatures drop well below freezing. To answer your question, fire ant response to disturbance will depend on how cold it is. At very low temperatures (below freezing), they are unlikely to come out if you disturb the mound. But just because they are not active on the outside of the mound does not mean that they will not come out if it is disturbed.

Here are some interesting papers on fire ant temperature tolerance if you want to read more:

James S. S., Pereira R. M., Vail K. M., and Ownley B. H. 2002. Survival of imported fire ant (Hymenoptera: Formicidae) species subjected to freezing and near-freezing temperatures. Environ. Entom. 31: 127-133.

Korzukhin M. D., Porter S. D., Thompson L. C., and Wiley S. 2001. Modeling temperature-dependent range limits for the fire ant Solenopsis invicta (Hymenoptera: Formicidae) in the United States. Environ. Entom. 30: 645-655.

Porter S. D., and Tschinkel W. R. 1987. Foraging in Solenopsis invicta (Hymenoptera: Formicidae): Effects of weather and season. Environ. Entomol. 16: 802-808.

Thanks for your question,
Ben Rubin & the AntAsk Team

Dear Ant Blog,

We have an in-ground pool with a concrete deck. Over the years, cracks have appeared as expected from expansion and contraction. Unexpectedly, ants have started coming in through these cracks. At one crack, there is a swarm of little black/dark brown ants who come out, sometimes holding little white objects, and throw themselves into the water. There they form into large clumps, about the size of a Ping-Pong ball, and float around. We have also noticed larger ants that we think are guard ants. We tried to take photos, but the camera kept focusing on the bottom of the pool instead of on the ants. One theory we had was that this might be a way of starting a new colony. Just float off with some eggs and guards and start up where you land. Also, when we scooped one clump out with the skimmer, it promptly dispersed and the ants began swarming towards the hand holding it. This hasn't happened before, and we have been here for several years. Do you have any explanation?
The Lawtons


Dear Lawtons,

Thanks for your interesting question and observation. We have deferred to colleague that happens to have quite a lot of experience with ants in the Gainesville area and with Solenopsis invicta, the Red Imported Fire Ant (which is what you are finding in your pool). Here is what Lloyd Davis had to say:

"The ants appear to be the Red Imported Fire Ant, Solenopsis invicta.  This species was introduced into the Southeastern US sometime between 1930 and 1950.  It came from South America, probably near Argentina or Brazil.  In its native habitat, the area surrounding a nest may be subject to unpredictable flooding.  These ants will cling to one another when flooded out of the nest or if they are trailing and fall into water.  I can't tell you why they ended up in your pool.  It is possible they were attempting to get to some other kind of insect that had also fallen into the pool."

You can read more about fire ants here, here, and here.

In addition there is a great video about this behavior of fire ants from the BBC, which can be watched here.

Thank you for contacting us,
Lloyd Davis (guest expert), Corrie Moreau & the AntAsk Team

Dear AntAsk:

My sister lives in St. Thomas, USVI. She writes the following:
"I have ants sometimes walking across my sofa. Have you ever heard of two different sizes of ants working together? Mostly they are tiny, but there are quite a number, maybe 1 in 10, which are about 3 times as large. They don't act like they're on different teams, and they seem to lug crumbs along the floor together. Never seen such a thing."
Neither have I. Any thoughts?

Dear Owen (and Owen's sister),

Thanks for your question. What you're seeing is most likely an ant in the genus Pheidole. Pheidole megacephala is probably the most common ant seen in people's houses that has two distinct sizes (such ants are referred to as dimorphic). The larger workers, sometimes called "majors" or "soldiers" have huge heads, and usually stay in the nest, but will come out to help the smaller workers when a particularly delicious (high in protein and/or fat) source of food is discovered.

There are several groups of ants whose workers come in more than one size, or caste. Ants have workers that are continuously variable in size (like carpenter ants, genus Camponotus, and Solenopsis invicta, the Red Imported Fire Ant) , or have more than two castes (like many leaf-cutter ants, especially in the genera Atta and Acromyrmex ). Such ants are referred to as polymorphic.

I hope this helps!
Jesse Czekanski-Moir & the AntAsk Team


I am an undergrad student from the Philippines and my thesis is about Ant diversity and their possible potential of being bioindicators of disturbance in an area. I would like to ask help from you guys for any related literature about ants here in the Philippines. Anything will help me a lot, be it about diversity, foraging, or other indication studies about ants published. 

Please help me.

Thank you.

Dear Rafael,

Thanks for your question. That's a really interesting topic, and there has been quite a bit of research into the use of ants as bioindicators. I'm not aware of any research that has specifically focused on the Philippines, but I can give you some citations of relevant studies from nearby areas like Borneo (e.g., Bruhl et al. 2003) and Papua New Guinea. It is further away, but some of the best Ants as Bioindicators work has been done in Australia.

But first: Anyone considering using ants as bioindicators, or sampling a large amount of leaf litter ants for any sort of ecological question, should read this book:
Agosti et al., 2000. Ants: standard methods for measuring and monitoring biodiversity
It is available here almost in its entirety for download in pdf form.

A recent paper that deals with statistically sound ways of sampling ants was just published in Myrmecological News:
Gotelli et al. 2011. Counting ants (Hymenoptera: Formicidae): biodiversity sampling and statistical analysis for myrmecologists.

Regarding Philippine ants, there was a very useful revision of the genus Odontomachus in that same issue of Myrmecological News:
Sorger, D.M. & Zettel, H. On the ants (Hymenoptera: Formicidae) of the Philippine Islands: V. The genus Odontomachus Latreille, 1804
Another recent revision is by Zettel (2006) of the genus Pristomyrmex.

Of the few works to be published about Philippine ant assemblages in the past 50 years or so are:
Way et al. 1998
Samson et al. 1997. Ant Diversity and Abundance along an Elevational Gradient in the Philippines. , and this one that might be useful with regards to the negative indicator species described below.

There is also, I might add, an excellent list of ants from the Philippines here and a useful key to their identification here.

That being said, you should try and do as much reading as you can about other case studies in which ants have been used or proposed as biomonitoring tools. For those readers not yet familiar with the "Google Scholar" search tool within Google, it is an excellent supplement to and even substitute for most online literature search engines. Click here for results relevant to this post.

Of the many articles that are retrieved, one of the most useful for justifying the use of ants as bioindicators is by Majer et al. 2007

Perhaps my favorite study on the subject is Anderson et al.'s 2002 Using Ants as Bioindicators in Land Management: Simplifying Assessment of Ant Community Responses. Anderson and colleagues clearly articulate one of the most important things to look for in a biomonitoring protocol: feasibility. "Will we actually have the time and expertise to continue this protocol, or is it so elaborate that we're dooming ourselves to a one-shot deal?" That is a very important question to ask.

In my mind, there are four main styles of using ants (or any other organisms) as bioindicators:

Umbrella species - make sure these species are protected, and all other species will be safe. Their absence should send out warning alarms. This approach is essentially the "Spotted owl" approach that environmental activists in the Northwestern United States used to justify saving big trees. From an ecological standpoint, it makes sense to select species that are very sensitive to disturbance, because that way, if they are safe, everything is safe. The logic of the umbrella species is that you want to take the most sensitive, asthmatic canary with you when you descend down that coal mine. With respect to ants, umbrella species would be tricky to use in a place like the Philippines because many of the most sensitive ants will be undescribed species, and it will take years to establish their identity. However, if there are known rare endemic ants on a particular island, this approach might be helpful, especially in combination with another outlined below.

Negative indicator species (NIS)- Bad Species! No! Go Home!
Negative indicator species should not be there. If you find them somewhere, then something is wrong. In many areas around the world, invasive species are present where ever there is human-caused disturbance. They themselves are also a force of ecological change. Five species of invasive ants (Anoplolepis gracilipes, Linepithema humile, Pheidole megacephala, Solenopsis invicta, and Wasmannia auropunctata) are among the 100 worst invasive species world-wide, and each have been show to change ecosystems in their introduced range. These species are excellent candidates for inclusion in a biomonitoring protocol in an area with many unidentified species, because they can often be unambiguously assigned a taxonomic name and an ecological value. In the Philippines, two out of the five have been reported so far: Anoplolepis gracilipes, Phediole megacephala. Those two and a third, Solenopsis geminata, might make good candidates for use in a negative indicator species biomonitoring protocol. And certainly any of the other ones would be worth watching out for if they were to show up. The satisfying thing about NIS as opposed to umbrella species is that when an NIS appears there are two proactive things you can do: try to figure out what went wrong with the environment to let the NIS in, and try to eradicate the NIS from its new range. When your umbrella species starts to decline or disappears altogether, you're often left with fewer clues and, well, no more umbrella.

Functional groups (at or above the species level)- This is when you look at a bunch of different species in a particular group (say, ants, for example) and check to make sure everyone is there. Or, you look at the average value for some trait of that group, or perhaps make sure that the group displays some ratio of traits. People who study rivers and streams in North America have shown that there are certain taxa, that are usually present when streams are unmodified and unpolluted. Because ants, as a family, display a wide variety of ecological roles, they can also be divided up into functional groups, and a characteristic combination of those functional groups should be present in each ecosystem. Australia has a very strong ant research tradition, especially in applied ecology, and the Australians were the first to follow the stream biologists and apply the functional group concept to ants. You can read more about the functional groups of ants here and here
Unfortunately, the functional group model of ant community composition is based upon the ants of Australia, and Australia's ants, like many of its other organisms, are quite distinctive. So a functional group approach to biomonitoring will not always be productive outside of Australia, unless perhaps new functional groups are established in each new place. Because relatively little is known about Philippine ant assemblages, it might be more productive to use a more generalizable approach, like Negative Indicator Species or fluctuating asymmetry (below).

Assemblage properties (of individuals) - Finally, there are some studies that deal with properties of individual organisms, specifically, asymmetry. Ants, frogs, and people are all pretty much bilaterally symmetrical. However, stress during development can cause slight abnormalities to occur, which make us more asymmetrical than usual. The key phrases for this line of research are "fluctuating asymmetry" and "Developmental instability"
Basically, one could take any group of normally bilaterally symmetrical organisms (even some plants and algae have been studied this way!), and measure the same thing on both sides of a lot of organisms. For insects, good things to measure might be eye width or wing length.

I hope this helps, Rafael. Biomonitoring is a very admirable idea, but difficult to accomplish effectively. Ants are a very strong candidate taxon for use as biomonitoring tools because they are very common in many different environments, and display a wide range of ecological preferences and tolerances. They are also fun and exciting to study! I hope you get a chance to look at some while you're writing your paper!

Jesse Czekanski-Moir & the AntAsk Team

Dear AntAsk,

I'm designing a behavioral experiment about nest-mate recognition in ants that I hope to publish in an educational journal. When I do the experiment with my class here in Oklahoma, I've been using harvester ants of the species Pogonomyrmex barbatus, but I understand this ant doesn't occur everywhere, and I'd like to offer educators from other areas suggestions for what kinds of ants might work.


Dear Stephanie,

That sounds like a really fun, educational activity! Pogonomyrmex in general are great to use, but here are some other genera that might be useful to people living outside of your region:

Formica spp. (wood ants) These ants are widespread in North America and Eurasia, and are often the most numerous large ants in boreal forests. They build mounds of vegetation (sometimes to 1m high or more) around their nest entrances.

Tetramorium caespitum (pavement ants). The most commonly seen ants on sidewalks in urban North America and Northern Europe. They often have nests with multiple entrances, so get ready to see some non-aggressive behavior, too. Ants truly from a different colony, however, will be violently rejected, and closely-spaced colonies of this species are frequently seen having all-out territorial wars (see previous post here ).

Aphaenogaster sp. and Messor sp. Also referred to has harvester ants, these ants have very similar habits and life-histories to Pogonomyrmex; all three genera co-occur, and are most common from southern California to west Texas.

The majority of ant species show some degree of internidal (between-nest) aggression, so most ants are worth a shot, with the following exceptions: most invasive ants. The Red Imported Fire Ant, Solenopsis invicta, is common and obvious from Texas to Florida. These will often not show aggression to other members of its species. The Argentine Ant, Linepithema humile, is very common in South and Central California; these ants rarely show aggression towards each other in their introduced range (there is actually a "mega-colony" that occurs in Japan, California, and the Mediterranean region in Europe; you can read more here ). Both ant species are originally from temperate South America, where they actually do often show internidal aggression. Many invasive ant species form polydomous and polygynous (multi-nest and multi-queen) colonies and show little internidal aggression in their introduced range, but have more "normal" nest structure, queen number, and levels of internidal aggression in their home ranges.

I did not really address how to identify these ant genera in this blog post, other than to direct you to some pictures. For an entry-level guide to identifying many of the relevant genera discussed above, please see this key, developed for the Bay Area Ant Survey.

For more in-depth information on ant identification, I would highly recommend checking out "The Ants of North America" by Brian Fisher and Stefan Cover.

Hope this helps!
Jesse Czekanski-Moir & the AntAsk Team

Fire ants in our area often form lines of mounds along a street curb. Today I noticed a different pattern. This pattern consisted of a dozen, or more, fire ant mounds spaced in a more-or-less equidistant distribution in a large mowed lawn. Space between mounds averaged about 20 feet. I assume that these mounds represent separate colonies? How does one account for the spacing? It does not appear to be random. Is there some mechanism by which some ants from a colony move to a new location in response to some stimulus? Is the adaptive advantage of this dispersal pattern related to food abundance? What initiates sub-colony movement: new queen, reduction in available food, some scent left by ants that builds up as they exploit a site? Have there been studies of fire ant behavior in relation to the resource base? If my observation is accurate, this behavior should maximize efficiency of resource use.


Hi Vincent,

Your observation of regular spacing among fire ant colonies is astute and similar to patterns you will see in lawns, pastures, and roadsides across the southeastern US, Texas, California, eastern Australia, and now parts of China. This natural patterning is a characteristic of dense monogyne (single queen form) fire ant populations. Each mound is the home of an individual colony with one queen. The space between colonies is "territory" which is divided up among adjacent colonies, usually in a rank order, where the largest colonies (which often have the largest mounds, too) occupy the largest territories.

Fire ants, especially the red imported fire ant, Solenopsis invicta, are one of the relatively few ant species that maintain absolute territories; that is, they guard and defend an area around the colony (mound), not just the mound itself, from any and all threats. Most other ant species defend only the nest, foraging trails, and food resources, so fire ants are a little unusual because of the amount of effort they put into maintaining their territories. Defense of a territory is probably an evolved response to intraspecific competitive pressure, that is, the fact that neighboring fire ant colonies are really good at competing with one another. The safest way to prevent having all of your food eaten or, more likely, your whole family captured and killed by neighboring fire ant colonies is to maintain a territory, remaining vigilant and defensive to any intrusion into the territory.

Maintenance of the colony boundaries is dependent largely on the interactions among a small number of individuals that scout around the boundaries of the territories. They respond to contact with non-nestmate ants by running away (in small numbers or as individuals, fire ant workers are actually rather timid when away from the nest). Thus, in zones of frequent contact at the edge of territories there actually exists a "no ants land" where there are very few individuals because they are "repelled" from one another by regular contact with non-nestmates. If they do not encounter ants from neighboring colonies they will, collectively, forage further and further from their territory. This thermostatic "control" of colony boundaries ensures that if, say, a neighbor colony suddenly dies, then its territory will rapidly be subsumed into one or more neighboring colonies' territory. As you can imagine, this kind of territoriality requires a large number of workers to maintain.

To the best of our knowledge, fire ant colonies generally do not appear to be resource limited or pathogen/parasite limited to the extent that it would drive frequent colony movements across populations. Fire ants, like most ants, are omnivorous and will opportunistically feed upon a wide range of food items. Colonies may, however, frequently be protein limited, but this does not appear to reach starvation levels that prompt a "move or die" scenario resulting from the resource base within the territory being completely depleted. Nevertheless, fire ant diet is an active area of research, as is territory maintenance. The best, and most complete work on fire ant territoriality has been carried out by my good friend Dr. Walter Tschinkel at Florida State University. Google him sometime and take a look at some of his papers or his book, The Fire Ants, if you would like to learn more!

Joshua King (guest expert) & the AntAsk Team

I live in the Northern USA and wanted to know if Fire Ants will ever be a pest in my yard?

The Red Imported Fire ant, Solenopsis invicta, is an introduced pest in the United States from South America. There are also native fire ants (species of the genus Solenopsis) found in many parts of the world, including the United States. Although the Red Imported Fire ant is an introduced pest in many parts of the United States, Australia, and some islands, it is unlikely you will ever have the invasive Red Imported Fire ant in the northern US since they are not able to survive long winters with hard freezes. Red Imported Fire ants are considered "hot climate specialists". This means they are unlikely to survive in your North Dakota yard, but may still be able to survive in places with temperature controlled environments like greenhouses. This species has even made the list of "100 of the World's Worst invaders":

Solenopsis invicta - Red Imported Fire ant. Photo by Alex Wild (

Where in the US are Red Imported Fire ants found?

The Red Imported Fire ant is thought to have been first introduced in the US in the late 1930's in the port of Mobile, Alabama. They are considered a serious problem due to many factors that include their ability to spread rather rapidly, their painful sting, aggressive behavior, and damage to some agricultural crops and livestock. In the United States fire ants have spread from Alabama across the southern US and into isolated areas of California, which has resulted in quarantines of movement of some products like soil and plants to help stop the spread of these invasive ants. Although we are not certain how much further north and west they will spread, we do know that they will not be able to survive outside in areas with long, cold winters.

Distribution of Red Imported Fire ants in USA. Map from:

Why are they called Fire ants?

Well if you have ever been stung by a Fire ant you can answer this question. Fire ants get their common name from the fact that when they sting you it feels as though you have been touched by a red-hot flame. These ants bite onto you (or other enemies, intruders or prey) with their jaws and then inject a dose of venom with the sting on the rear end of their body. Their sting is not only painful, but for some people this can be a real problem since it can result in anaphylactic shock or even death in very extreme cases. Also most people develop an itchy, puss filled bump after being stung.

Fire ant stings USDA.jpg

Fire ant stings. Photo from:

How can I identify a Fire ant?

Telling fire ants apart from other ants can be difficult since they look like most ordinary red/brown ants, although AntWeb and a microscope will help. Two of the key signs are their behavior (they are very aggressive and sting readily) and mound-shaped nests. Each of these mounds can contain up to 300,000 individual ants.

Fire ant mound AlexWild.jpg

Fire ant mound. Photo by Alex Wild (

Although this species is considered an invasive pest in some areas like the United States and Australia, it is important to keep in mind that they are not all bad. In their native range of South America it is one of many important ants in the ecosystem. For more information on the Red Imported Fire Ant, check out this webpage which contains many informative links:

- Corrie Moreau & the AntAsk Team



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