Ant behavior: November 2012 Archives

I teach at a high school in Australia and I'm currently doing a unit on ants. One of the students in the class lives on a farm where there are lots of black ants. He and his family (I spoke to his father after school and he confirmed that his son was not kidding) have observed that ants seem to know when the rains are coming "weeks, even up to a month before they actually arrive." He says that they start preparing by storing food and building up walls around the nest.

The class found this fascinating and wanted to know how the ants could possibly know the rains were coming so far in advance. I told them that antweb are an authority on ants and that I would write to you for an explanation. My first question is: Is it possible that the ants could know the rains were coming so far in advance? Secondly, if so, how are they able to do this. Thirdly, if the student and his family are wrong, what are they observing that leads them to believe that the ants are long term weather changes?

My class and I would greatly appreciate any insights you are able to offer on this topic.

Kind regards,


Dear Max,

Thanks for your question!
There are a variety of ways that human meteorologists can predict the weather: they can look at trends in barometric pressure, they can note the wind direction and look at the clouds (from the ground or from satellites). But they can also make general predictions based on past trends. I suspect that any meteorologist in your area could predict to the nearest 10 days when the first monsoon rains are likely to hit southeastern Queensland, and they wouldn't need any information at all about the current weather! In many areas of the world, there are predictable times of year that organisms need to prepare for or migrate away from--times of year that are either too cold, too hot, too wet, or too dry for organisms to function well. Some organisms whose ancestors have been living in those places for millions of years are adapted to the annual rhythm of these seasons. The ants your student and his family observed are not "predicting" the weather any more than migratory birds or blossoming flowers are--they're just behaving in a way that is adaptive to long periods of rainfall.

Many animals and plants (and perhaps other organisms, like marine algae) have an instinctual response to seasonal cues like light levels or day length (photoperiod). For example, cherry trees from certain parts of Asia will always flower when days are as long as they are at the beginning of spring in that part of Asia. For other plant species, budding occurs only after some threshold of both photoperiod and temperature has been passed, and bird migration may be regulated by an even more complex interplay of cues, including food abundance. It has even been proposed that organisms might have "circannual clocks," the annual version of our circadian rhythms that get messed with when we travel to a new time zone. For many species, the exact cues used to regulate annual cycles of behavior and life history (or phenology) are not understood.

I'm sure you've guessed by this point that I don't know exactly what cues the ants on your student's farm are responding to. But as a class, you might be able to perform some scientific experiments to figure it out! My understanding is that your rainy season is the Austral summer--the warmer time of the year, with longer days. Thus, two cues the ants might be using (separately or together) are the length of the days and the temperature. If there are many of these ant nests, then you could set up lights around some nests about half way through the winter, and put them on a timer so that they turned on a half hour before dawn and again a half hour after dark. Near other nests, you could place some "heat rocks," like those used for reptiles. Some nests could receive both treatments, and some nests neither. Then you could see if any of the ant nests "predict" that the rains will come earlier than others. Unfortunately, you might have to wait until next year to perform this experiment, but, hey, it doesn't hurt to plan ahead, right?

One reason phenology and chronobiology are such "hot" topics lately is that global climate change is likely to make things difficult for organisms that use photoperiod as a cue to adjust to the changing of the seasons. Perhaps you and your class (or future classes) could help us better understand how the ants of Australia will react to climate change!

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


How come when it gets really hot ants are still able to run around on bitumen and pavers without burning their feet?

Anna W

Dear Anna,

Although the thermotolerance of ant tarsi (feet) on hot bitumen or pavement has not been directly studied, there are a few biomechanic studies out there that can help us make some educated guesses.

Part of the reason ants may be able to run quickly over hot pavement is that their tarsi are composed of sclerotized chitin, which is a really tough polymer of many connected glucose molecules. The toughness of this biomaterial is often compared to the keratinized tissue seen in vertebrate hooves--such as horse hooves--many of which are also able to walk on hot bitumen and pavement. This is very different than human feet, which have many nerves and soft, burnable tissue on the bottom of our feet. Yet, even humans can walk on hot pavement if repeated friction and pressure forces the formation of calluses that insulate the sensitive tissue in your foot from the pavement.

While this explanation helps us understand how ants don't burn their tarsi (feet), it does not get around the larger of issue of how the ants on hot pavement deal with the increased body temperature (ants are small!). Well, as it turns out, there are some extremely interesting studies on ants that have adapted to hot, dry environments. One ant in particular--the Sahara Desert ant (Cataglyphis bicolor)--has adapted such a high thermotolerance that its proteins can operate at higher temperatures (4-5 degrees Celsius) and it can forage normally at body temperatures above 50C or 122F. Considering this ant makes a living by running on the hot sand to find and consume insects that have died of heat exhaustion, it makes sense that it can withstand this heat. While you wouldn't commonly find Cataglyphis running on pavement, there has been recent research showing that ants found in urban and suburban areas are more likely to come from hotter, drier habitats because of the prevalence of open areas in the urban and suburban landscape. Thus, it is logical that the ants you see running around on pavement might have also have some thermotolerance themselves!

Thanks for your question,

Max Winston & the AskAnt Team

Hi there!

I've recently observed a bunch of ants on my desk at my lab that seem to "freeze" in movement, in a group, usually in a straight (but not linked) line against the wall, completely stationary for hours at a time. They're usually gone by morning and they tend to return again, usually in the afternoon and the cycle repeats. I've been trying to read up for info on this online but I haven't found any information that explains this. These are small brown ants, common to households, but I'm unsure as to the exact species.

I apologise in advance for the lack of information but I'm extremely curious as to what causes this behavior.

Hope you can shed some light on this.

Thank you

Dear Felicia

The ants you saw are most likely Tetramorium bicarinatum, a species that occurs in houses world-wide. One of the other contributers has observed the "freezing" behavior in other ants, but we really don't know why they do this. It is possible they are responding to vibrations in the object they're standing on, and that freezing might make them less visible to predators. This is a behavior we really don't understand.

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

Acacia-ant mutualism?

Hi there.

I am a science teacher who traveled to Northern Kenya in July. While in Ndonyo Wasin (near Archer's Post), I observed many ant mounds under acacia trees. I was wondering if you could identify the type of ant that built this mound. I am also interested in learning more about their mutualism. I am writing a science curriculum about the environment that surrounds our sister school there, and would really love to learn more about the ants that inhabit the region. Any help would be greatly appreciated.



Dear Maria,

The mounds in your pictures were made by termites, not ants. They are potentially interesting for their complicated caste system and symbiosis with certain fungi, similar to Attine leaf-cutting ants in the Americas.

However, I am guessing that the mutualism you are referring to is that between acacia trees and ants, not between termites and fungi. Such relationships do occur in Kenya between Acacia drepanolobium and three species of ant in the genus Crematogaster and one species in the genus Tetraponera. Unfortunately, the plant pictured here is not an Acacia drepanolobium, but that does not mean they are not present in the area. These plants typically grow on "black cotton" soils and are often the only overstory plant in the area.

Acacia drepanolobium trees are very easy to identify because they are full of hollow swollen thorns and are typically rife with ants, as in the picture below.

Photo by Eric Denemark

The basic idea behind the mutualism is that the plants grow the hollow thorns pictured as well as extra-floral nectaries and protein-rich food bodies. Ants nest in the thorns and feed on the nectar and food bodies and in exchange, they aggressively protect their host plants against herbivores. The ants are so effective that they can even protect their plants against elephants (Goheen and Palmer 2010)! The ants will not nest anywhere else and without ant residents, the acacias are quickly destroyed, making the mutualism obligate. Both organisms involved are completely dependent on each other. However, when researchers (Palmer et al. 2008) used fences to exclude large herbivores from a plot of acacias for a period of ten years, the plants actually stopped producing resources for the ants, because they no longer needed their protection. Without their host plants, these ants have nowhere to nest. This is yet more evidence that the extinction of single species can have wide-ranging and unexpected results.

In reality, the acacia-ant mutualism is much more complex than what I have outlined. For example, there is a high level of competition between ants of both the same and different species for nesting space because nearly every tree is occupied and founding new colonies or expanding current colonies necessarily means that confrontation must occur. The dominance hierarchy between species is closely related to average colony size (Palmer et al. 2000). No single ant of a species involved here is much better at fighting than any other ant so the largest colony usually wins. Ants also provide differing levels of protection to their hosts so plants experience different benefits depending on who is nesting in their thorns.

If you do find these plants and ants in the area, I would strongly encourage you to incorporate them into your curriculum. The four species of ant are easy to tell apart by the shape of their body and coloration of segments. See how the first two segments are red and the last segment is black in the ants in the picture? That means they are C. mimosae. C. nigriceps is black, black, red and C. sjostedti is all black. The single Tetraponera species, T. penzigi is also all black but has a long and thin body unlike the stocky Crematogaster species.

As you may have guessed, a lot of research has been done on the Kenyan acacia-ant relationship, predominantly by Todd Palmer's research group at the University of Florida and Maureen Stanton's group at the University of California Davis. I have listed a number of their publications below but you should definitely check out their websites as well. They have been featured in quite a few popular science articles that may be useful.

Thanks for your question and good luck,
Ben Rubin, James Trager & the AntAsk Team

Goheen JR, Palmer TM. 2010. Defensive plant-ants stabilize megaherbivore-driven landscape change in an African savanna. Current Biology 20, 1768-1772.
Palmer T. 1994. Wars of attrition: colony size determines competitive outcomes in a guild of African acacia ants. Animal Behaviour, 68, 995-1004.
Palmer TM, Brody AK. 2007. Mutualism as reciprocal exploitation: African plant-ants defend foliar but not reproductive structures. Ecology 88, 3004-3011
Palmer TM, Stanton ML, Young TP, Goheen JR, Pringle RM, Karban R. 2008. Breakdown of an ant-plant mutualism follows the loss of large herbivores from an African savanna. Science. 319, 192-195.
Palmer TM, Young TP, Stanton ML, Wenk E. 2000. Short-term dynamics of an acacia ant community in Laikipia, Kenya. Oecologia, 123, 425-435.
Stanton ML, Palmer TM. 2010. The high cost of mutualism: effects of four species of East African ant symbionts on their myrmecophyte host tree. Ecology 92, 1073-1082
Stanton ML, Palmer TM, Young TP. 2002. Competition-colonization trade-offs in a guild of African acacia-ants. Ecological Monographs, 72, 347-363.

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