February 2013 Archives

Dear askantweb,

I found what seems to be an undocumented army ant while camping in San Diego County.

Doing my best to remember, I recall these characteristics of the species:


  • Completely black
  • Worker, major worker, and soldier classes
  • 5 cm to 10 cm long
  • Soldier mandibles appear to be able to make an audible snapping sound

  • Behavior:

    • Forms columns at night moving in one direction
    • What seems to be scattered scouts mostly of the worker class preceding the main column mainly observed just after sunset
    • Invades the local termite colonies
    • A number of ants were found to be dedicated to what appears to be guarding an entrance of apparently a subterranean nest at the base of a tree. This was observed during the day and the only instance of observing this specie during the day except when excavating a known local termite colony which was being attacked or occupied by these ants.

    Though it could simply be a carpenter ant, please advise or forward to anyone who may be interested. Thank you.

    Dear Spencer,

    If the insects in question are really 5-10cm long, it's pretty unlikely that they're ants. We have a blog post on how big ants tend to get, and California I can't think of any ants that would be much bigger than 2cm, even if they were a queen.

    There are actually quite a few documented species of army ants from California. The genus Neivamyrmex has workers of different sizes, but they're kind of continuously polymorphic, so you'd be unlikely to think of them as "worker" "major worker" and "soldier." I have a little bit of experience with army ants from the tropics, and I've never heard them really snap.

    The only genus I've heard make an audible snapping noise is Odontomachus, seen here closing its jaws. This genus hasn't been recorded from California as far as I know, but it's possible that the species found in Arizona could make it in SoCal. However, these ants are all the same size as each other, so you wouldn't have noticed distinct castes.

    Carpenter ants, (genus Camponotus) are also large and polymorphic. If you were close to a lot of them, you might have noticed a vinegary smell (formic acid). None of the other ants I've just mentioned would have made that smell.

    Ultimately, I guess I'm stumped. If you go camping again, be sure to take some pictures!

    Jesse Czekanski-Moir & the AntAsk Team

    I'm sure you get a lot of questions phrased like my subject heading. But I'm stumped here! I've linked to two pictures I took in the woods in Atlanta, GA.



    From the far shot, it looks like the ants are "herding" the insects into a big clump. in the closer shot, you can see that some ants have actually dived into the fray.

    Were these ants really herding the other insects or had the insects been swarming beforehand and the ants are just there to pick some off as food?

    Also, I can't seem to identify the insects in the pictures that the ants are interacting with. They look like some kind of insect in the nymph stage.

    If it matters, the tree in the picture is a beech, I think.

    Thanks for your help! I'm so glad I found this blog!


    Dear Becky,

    Thanks for the great pictures! Yes! Many ant species have facultative mutualisms with aphids (seen here) and other herbivorous insects. The ants guard the aphids from predators, and, in exchange, the aphids essentially poop sugar water into the ants mouths. This "honeydew" as it is euphemistically called, has to be voided from the aphids, because they have to go through a lot of plant sap to get enough minerals and amino acids. To the ants, it's gatorade.

    The ants are most likely the common carpenter ant, Camponotus pennsylvanicus. I don't know much about aphids, but those are really big, and they seem to be on the bark of a deciduous tree, so they might be the giant bark aphids, Longistigma caryae. There're probably some other big aphids out there, but this seems to be a pretty widespread, conspicuous species, and they have been reported to associate with C. pennsylvanicus elsewhere in the Southeastern United States.

    There have been a few posts about this relationship in other blogs (such as here and here ) and there's a rich scientific literature of ant-aphid mutualisms you should check out if you'd like to know more! There are also some pretty great photos that have been posted by others!

    Thanks again for your great pictures!


    Thanks for taking the time to answer my question. I was recently traveling in Costa Rica and happened to take a camera shot of some interesting ant behavior. I have no idea what is going on here, but would sure like to find out. Have you ever seen this kind of behavior before? (see attached image)

    Please let me know.





    Great image! What you have documented here, quite beautifully, is a number of Azteca workers "spread-eagling" a Pachycondyla gyne (future queen). This is an interesting and well-known behavior of the genus Azteca (Dejean et al., 2009), which is well known for its mutualistic associations with plant species (Cordia, Cecropia). The mutualism between the plants and the ants relies on the plants providing food and shelter to the ants, and the ants fervently defending the plants from herbivores and other competitive plants. This behavior, known as "spread-eagling", is usually employed by the workers to protect the plants from insect herbivores or intruders, and is not restricted to the plant alone.

    Because the Pachycondyla gyne has not started her colony yet and become a queen (you can tell because she has not dropped her wings yet), it is likely that the Azteca ants are showing this aggression to defend their territory before she can start a colony and get a foothold in their area. Although the pictures don't show it, I'm guessing the gyne did not escape alive.

    Hope this answers your question, I've included the reference below.


    Max Winston & the AskAntTeam

    Dejean, A., Grangier, J., Leroy, C., & Orivel, J. (2009) Predation and aggressiveness in host plant protection: a generalization using ants from the genus Azteca. Naturwissenschaften. 96:57-63.

    Dear Ask Ant Team,

    I was reading about geosmin, produced by bacteria and released when they die and which gives a distinctive smell after rain.
    Geosmin is very strongly aromatic and some researchers believe that humans can smell this compound at low levels of 5-10 parts per trillion. Others believe that geosmin enables camels to find water over distances of up to 50 miles.
    Is there any research which shows that ants in arid dessert environments use geosmin to locate water?
    Many thanks for your help.

    kind regards,

    Dear Ian,

    Thanks for raising this very interesting question! In an article from 2002, researchers discovered that millipedes, not only bacteria, can produce geosmin. They tested the effect of geosmin on ants and found that ants were not affected. However, millipedes of the same species were repelled by geosmin. The researchers concluded that it plays a role for chemical comminication in millipedes. Apart from this paper, I am not aware of any studies that tested the effects of geosmin on ants. This would be interesting, because there are many different ant species which likely show different responses to this chemical. This is indeed an interesting topic!

    This is the paper:

    Omura, H; Kuwahara, Y; Tanabe, T (2002) 1-Octen-3-ol together with geosmin: New secretion compounds from a polydesmid millipede, Niponia nodulosa. Journal of Chemical Ecology 28(12): 2601-2612.

    All the best,
    Steffi Kautz & the AntAsk Team


    First of all, many compliments for your blog: it's awesome and full of interesting and useful info. Secondly: I'd like to set up a competition experiment of two ant colonies in a formicarium I'd build myself. I'd like to see how the two different ant species will use and exploit the resources and see how competition happens. Could you help me set up the experiment? For example, what two ant species from Europe should I buy and use in the experiment? Can I set up the formicarium so that the food is in a central chamber? Will the ants find their way to the food anyways? What would other interesting things to observe be? Would the "competitive exclusion principle" work? . I live in italy and a local retailer has Camponotus nylanderi, what could i match with this?

    Thank you so so so much!

    Hi Alessandro,

    Thank you very much for your question!

    Antweb has a site on the Ants of Italy that you can check out to find out which species occur in your area. There are many ant species that you could try for your experiment. I would suggest that you collect a local species. Ant queens often swarm in the summer and you could get your formicarium ready for that and then start out a new colony.
    If you do not want to wait for the queen to establish a new colony, here is a post on how to collect an entire colony. We also have this extensive post on how to make an ant farm with suggestions on how to collect queens and establish a new colony.

    You could set up your formicarium with three chambers, which are connected by tubes. The chamber in the middle would have the food and either chamber on the sides could have one of your ant colonies. However, I would assume that in any case, the two different species will kill each other until one colony has been eliminated. For some ant species, fights are one-on-one usually leading to death of both workers involved in a fight. Thus, the colony with more workers wins. Some ant species, particularly invasive species, are often more aggressive than native species and might outcompete them. Small ants sometimes fight in groups. There are so many different ant species, each with their distinct behavior, that it is really hard to predict the outcome. In any case, I assume that such an experimental set-up will lead to fighting ants.

    I hope this helps,
    Steffi Kautz & the AntAsk Team


    I stumbled across your very interesting blog whilst searching for an answer about ants.

    We live in the sub-tropics (Queensland, Australia) and just over a week ago experienced severe wet weather (flash flooding) due to an ex-cyclone passing over us. This was after an extended period of dry weather in a hot Summer. We have had a steady stream of various ants come in due to the weather, mostly heading for the kitchen. This is quite normal for us and has been managed mainly by keeping minimal accessible crumbs etc.

    The unusual ant activity we've had is in the last couple of days. One night we suddenly realised that there were clumps of tiny black ants all over the house. There were thousands of them in the laundry, on the top of the wall and cornice - not many down near the water sources at all. There were also about 6 big clusters of them located on cornices throughout our living room and hallway - far from any food source and/or water. The next day another cluster appeared on the door frame of our bedroom en suite - these ones were near some artwork and some were feasting on the glue used in it, but most were in clumps on the doorframe. I took some pictures and have attached them.

    Ants1 is to give you a reference point for size and the shapes of all the small clusters these ants are forming - these are very small ants compared to most others we get locally.
    Ants2 is a closer shot - when I was later looking at the photos I noticed that the ants appeared to be clustered around some sort of larvae or white-fleshed ant? I suppose this is why they are clumping, but am wondering what the white things are. I am hoping it is not termites! I am also curious as to why these ants all suddenly appeared in such unlikely places (and so many times) particularly given that it had been about a week since the wet weather. I would also like to know what we can do to try and discourage them from invading our house in such a huge and sudden manner.

    I've done some searching on ant identification pages etc. and the closest ant I can come up with that they may be is the "black house ant". Although I am not sure they have the right number of joins in their body.

    Any answers to my questions would be much appreciated!

    I can send a bigger sized picture if you require it, just let me know if you do need it. I just didn't want to unnecessarily overload your inbox with a large sized file.

    Thank you,




    Dear Anna,

    Thanks for the question and the pictures!

    First off, these are definitely not termites. Note the "elbowed" antennae and distinct rear part of the body (called the "gaster" in ant literature).

    These ants probably belong to the genus Technomyrmex. They're very common in forests in tropical Southeast Asia and Australia. I used to work on a small group of islands called Palau, and there were parts of the forest where it seemed like nearly every tree had this density of Technomyrmex on them. Although it's tough to say for certain, it's likely that these ants belong to a group of very similar-looking species that would have all been identified as Technomyrmex albipes a few years ago, but have since been shown to belong to several distinct species, including T. difficilis (guess why it has that name!). Here are some close-up pictures of the ants I think you have (although this this ant is fairly widespread, these pictures were actually taken in Queensland). In your region, many common household ants can be identified using a key developed by Eli Sarnat for the Pacific Invasive Ants program out of New Zealand (assuming you have a good microscope). For more complete information on ants in your area, check out our Queensland section on AntWeb, and Steve Shattuck's Ants Down Under.

    We've written a few posts about getting rid of ants in and around your home (for example: here, here, here, and here), but in your case, one of the more important actions might be keeping vegetation from touching your house. I've actually seen a house in Palau that was entirely on concrete stilts, and each stilt rested on a concrete block that had a small moat of water in it - this is essentially the house-level equivalent to putting the legs of your kitchen table in tuna cans filled with water to prevent ants from climbing up. However, the house got electricity from an above-ground wire, and there was a steady stream of Technomyrmex coming in on that wire all the time! So....I guess there's only so much you can do!

    Hope this helps, and good luck!
    Jesse Czekanski-Moir & the AntAsk Team

    I am doing a class project on ants and I am just wondering is there anything that ants do not like to build nests near or close to, I know they like to build nests on geopathic stress lines but is there anything that they don't like to build on?
    kind regards,

    Hello Joseph:

    Thanks for your question to the Ant Blog! For the first part of my response, I'd like to say that different sorts of ants, among the almost 14,000 species known, have different nesting preferences. So, for example, one would not find characteristically arboreal ants nesting in soil, nor would soil ants nest under bark of a living tree. Some species prefer particular soil types, such as sandy and well drained, or dark, moist and rich. At larger scales, grassland ant species are unlikely to be found nesting in a forest, nor tropical ants in a region with a winter season.

    But, I'm guessing that your question refers to species of "generic" soil-nesting ants. These often appear not very fussy about where they locate their nests. Such ants may be found nesting in soils with all sorts of textures and moisture levels. Studies have demonstrated that there are ants nesting at nuclear bomb test sites, where toxic metals have been mined, and areas reduced to ash and heat-sterilized soil by wildland fires. I've even found nests of ants in soil so toxic that no plants could grow in it, on military land, created by incineration of "unexploded ordinance".

    On the other hand, one consistent pattern I've noticed over the years is that soil nesting ants do not usually nest in soils that are compact and saturated (covered with water) after rains. For example, the lawn around my house has patches with numerous ant nests, and others where there are none. After heavy rains, it becomes clear that the ant-free zones are slightly lower, and water pools in them for a while before soaking into the ground or evaporating.

    James C. Trager of the Ask Ant Team

    Hi guys,

    First of all: this blog is really helpful, great work!

    So now, while trying to write a report on ants --focusing on aspects of evolution-- I stumble upon many many questions. I'm hoping you can help me out!

    1a. Micro-evolution
    I was thinking about invasive species that are nowadays found in several continents, like for instance the Argentine fire ant.. Do all of their populations still belong to the same species? (no subspecies)
    If so, how come? And would a male and female both from a different continent still recognize each other as potential mating partners or not. (If not, what's the term for that?)

    What are specific factors that trigger origination of (sub)species of ants, or what causes the absence of it.

    1b. Macro-evolution.. Can we speak of macro-evolution within the ant family, since there are so many different varieties. If not, could the relation between wasps and ants be an example of macro-evolution or is macro-evolution really about even bigger events?

    2. Sexual selection
    In the mating of ants, is there any 'conscious' selection going on from either gender. Are there species where an individual for mating is picked over another, based on qualities perceived?

    Thank you!

    Greetings :)

    Dear Zoe,

    Thanks for your questions! You've gotten to some really awesome, fundamental evolutionary biology questions here, and you're asking me to make generalizations across a family of insects with more than 100 million years of evolution and more than 10,000 species, so I'm not sure I can do them justice in a blog post, but I'll try!

    Your sub-question under heading 1a: "what are the factors that trigger origination of (sub)species of ants, or what causes the absence of it," is a question that can only be answered in a very generalizable way: speciation occurs when some factor causes populations of organisms to begin separate evolutionary trajectories. Often, as you suggest with respect to invasive species, this happens because of geographic isolation (allopatric speciation), but there are many theoretical and empirical studies that allude to the possibility of sympatric speciation, which is when speciation happens while populations of organisms are still within "cruising range" of each other. A previous blog post elaborates on speciation in the context of nest parasites.

    Your first question about invasive species is great and very timely! There have been at least two studies in the past few years which demonstrated that Argentine ants (Linepithema humile) from different continents actually recognize each other as nestmates! So I can't imagine there would be any trouble with mating there.

    The authors of both papers suggest that nestmate recognition is maintained across different continents because there is a steady stream of new arrivals, which prevents the populations from drifting apart. However, the question of when exactly a speciation event happens is very difficult to pin down. In a classic paper on the "Evolutionary species concept," the icthyologist EO Wiley states that "A species is a single lineage of ancestral descendant populations of organisms which maintains its identity from other such lineages and which has its own evolutionary tendencies and historical fate."

    By this definition, you would really have to be able to predict the future: how can you know whether a newly isolated population will come into contact with propagules from its ancestral range? The idea that newly isolated populations are incipient species is tempting, but in practice, species can only be delimited if there are morphological and/or molecular differences in them, or, if you subscribe to the biological species concept, things could be argued to be different species if they generally choose not to mate with each other (for more information, you might want to look up pre-zygotic isolation and assortative mating...). In the case of the Argentine ant, I would expect a sudden drop in propagule pressure would result in the actual isolation of the disparate populations, but I would only expect this to happen if humanity drastically changed or ceased its practice of global trade and travel.

    Sexual Selection
    Speaking of pre-zygotic isolation and assortive mating, I think it makes sense to talk about sexual selection in the context of micro-evolution, because that's potentially a pretty important driver of speciation and trait evolution in sexually-reproducing organisms. Stearns and Hoekstra, an often-recommended text in evolutionary biology, defines sexual selection as: "The component of natural selection that is associated with success in mating." While at first somewhat disappointing, I think this definition is useful because it underscores the fact that sexual selection is a component of natural selection. Many ants form mating swarms, or leks, especially in desert and temperate zones. In these cases, there is a certain amount of "scramble competition," and differential levels of mating success have been demonstrated to correlate with individual traits. However, I am not aware of anything approaching the level of mate choice and the resultant secondary sexual ornamentations that has been demonstrated in some butterflies, odonates (dragonflies and damselflies), or other animals.

    For a variety of reasons, the exaggerated secondary sexual traits that seem to emerge in classical examples of sexual selection (i.e., the tail of male peacocks) seem to be less likely to develop in eusocial insects (for a more in-depth perspective on this, check here, here, and here). In lekking species, there is likely to be a very important trade-off between the relative sizes of the flight muscles and the testis and ovaries. Some species of ants do not lek, and either engage in within-nest mating (intranidal mating: for example, some Cardiocondyla exhibit this incestuous behavior), and others engage in "mate-calling," like some moths. For these species, ability to give off (for the females) and recognize mating cues (for the males) is likely to be selected upon, but, to the best of my knowledge, selection on particular traits in these species has not been selected upon. By Stearns and Hoekstra's definition, sexual selection is likely to occur in any sexually-reproducing species, regardless of escalating selection for mate-choice.

    I'll defer to Stearns and Hoekstra again for their definition of macro-evolution: "The pattern of evolution at and above the species level, including most of fossil history and much of systematics." By this definition, macro-evolutionary patterns are evident in any taxon above the species level, for example, the fact that genera such as Pheidole, Strumigenys, and Camponotus have many species, while Paraponera, Tatuidris, and Rostromyrmex have very few species is a macro-evolutionary pattern. More ant genera than usual seem to have arisen when the earths terrestrial vegetation came to be dominated by flowering plants, which is another macro-evolutionary pattern.

    Traits can also exhibit macro-evolutionary patterns: ants are all eusocial - we don't know of any solitary ants. Asexual reproduction has cropped up several times in a variety of ant lineages, but does not seem to have persisted beyond a speciation event. The ability to cultivate fungus has only occurred once in the ants. The processes that gave rise to these patterns are somewhat outside of the realm of macro-evolution, but the justification for using the term "macro-", instead of referring to these patterns as just plain old "evolution," is that they cannot be predicted by an understanding of intra-specific evolution alone. This is analogous to the anti-reductionist argument that cell biology cannot be usefully predicted by chemistry alone--simply understanding osmosis and organic chemistry would not allow us to predict the utility of sexual reproduction, which in some situations can give rise to heterogamy, which in turn drives the emergence of a fertilization envelope, uniparental organelle inheritance, and, in one case, the tail of the peacock. In another case, irreducible patterns and processes random-walked their way to the population of weird little wasps that would become the ancestors of all ants.

    As I said at the outset, one would need quite a bit more time and space to fully answer your questions, but I hope I've at least given you some food for thought.

    Jesse Czekanski-Moir & the AntAsk Team