Recently in Ant behavior Category

Dear Ant Blog,

All the photographs I see show ants using their mandibles like tongs. Can they rotate them like we can rotate our arms?

Katrina

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Dear Katrina,

Despite the fact that ants use their mandibles for a multitude of different functions including prey capture, manipulation, and escape, there are no ants that have been proven to have fully rotational mandibles. Humans have a ball-and-socket joint that allows great range of motion, and although ants have a ball-and-socket joint for their antennae, their mandibles usually have a single plane of motion. Although this limits range of motion, it allows for much greater strength.

In case you are interested in reading more about mandibles, Chris Schmidt wrote a basic introduction to mandibular function as a part of the Tree of Life project. There are also several academic papers that detail the movements of mandibles (see Jurgen Paul), as well as some of the most extreme mechanical "trap-jaws" that have been convergently evolved by several ant species.

Hope this answers your question!

Best,

Max Winston & the AntAsk Team

Hey, AntAnswerers!

So, I've been thinking a bit about the situation with trophic eggs in ants. It apparently seems a pretty common practice among ant queens to eat some of their unembryonated eggs. Fair enough.
What I don't understand is the energetics of this practice- calorie for calorie, wouldn't it be costing a queen more to produce these trophic eggs than she is gaining from eating them?
I could understand making the best of a bad situation (i.e., for other arthropods that overshoot the optimal number of offspring, cannibalism retrieves some of the calories from a previous, poor decision), but I'm not sure that kind of argument applies for ants. Any thoughts from you guys?

I am similarly confused about the energetics of dracula ants, for similar reasons (i.e., the food comes from within the "extended phenotype").

Many thanks!
-Mark

Dear Mark,

Typically, trophic eggs are unfertilized eggs laid by workers and used predominantly to feed larvae and queens but can also be fed to other workers. This type of resource sharing is similar to the regurgitation (trophallaxis) that occurs frequently between ants that you may be more familiar with.

Queens can also produce trophic eggs and new foundresses often use these to feed their young larvae. They certainly could eat these themselves and they may be useful as a way of storing food until it is needed, but most are fed to their offspring.

Also, larvae do sometimes cannibilize other larvae as you mention. This system of feeding larvae may or may not be optimal for the colony but it undoubtedly benefits the larval aggressors.

Dracula ants are incapable of consuming solid foods because their mouthparts are not built for chewing. The larvae, however, can consume and digest these foods, producing a resource rich hemolymph. Many ant colonies operate in this way, indirectly feeding on the digestive capabilities of the larvae. Dracula ants are special because the larvae do not have the ability to regurgitate nutrients and must, therefore, be bitten open by the workers. Larvae of most other species are perfectly capable of regurgitation so this complicated method of sharing resources is not necessary.

Great question!
Ben Rubin & 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.

http://www.flickr.com/photos/65837114@N00/7578847944/

http://www.flickr.com/photos/65837114@N00/7578844086/

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!

-Becky

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!
best,
Jesse

Hello!

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.

Mike

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Mike,

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.

Thanks,

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.

I am a typical mom who knows only three things about ants: they have structured colonies, they carry 3x their weight, and they invade our home during the rainy season. I had never noticed this behavior before and came upon your website in trying to research if what i think is happening is true. The black ants that I see in my bathroom are scouting for food and I don't kill them because I know they will not find any and will eventually leave, but some lone ants have become lost or stranded and I will see them roaming in the same area for a day or two and then they seem to die. Is it from starvation or cold temperature at night, or emotional distress at being alone with no way back to what they know as home?
Also, when they first invade there are many following a trail but soon I see that some break into groups of a dozen or so that scatter when they detect me, do they communicate in this way? I thought they were more like little robots following programmed instincts so they used chemical scent trails, but it almost looks to me like they are having a meeting to discuss their options. I use Clorox wipes to clean and have looked at the spot were they grouped to make sure there wasn't anything that could have served as food like my son's bubble gum toothpaste. I hope to learn more as I respect these tiny hard workers.

Thank you!
Claudia from central California

Hi Claudia,

Rather than thinking of ants as robots following programs, it might help understand what they are doing by imagining them as small people with a limited view of the world and very short-term memories. Contrary to popular belief, no single individual is in charge of an ant colony, not even the queen. Instead, an ant colony's behavior is accomplished through the independent action of each individual together. So every ant has to use the relatively small amount of information available in the immediate area to figure out what she should be doing. Oftentimes, this means "asking" other ants what they are doing and if they have an opinion on what everyone else should be doing. This type of communication is usually accomplished through antennal contact and scents and could certainly result in the formation of groups of ants all "talking" to each other, figuring out what they should all do next. Of course, it is always a possibility that they just found something interesting on the ground.

The ants that you find in your house are almost certainly looking for food. They could also be exploring for new nesting sites and, as your house is probably relatively warm, it might appear ideal at first. Unfortunately, no matter the reason for their exploration, foraging ants have very high rates of mortality around 15% per day. Many of these ants are the victims of predation or, in hot and dry areas, dehydration, but many simply get lost, as some of the ants in your house seem to. A scent trail may be too faint, may get disturbed, or the ants may get separated from it inadvertently and be unable to find their way home. Their eventual death is likely the result of starvation or dehydration although cold temperatures could certainly be a factor as well.

Deborah Gordon's book, Ants at Work is about how ants get all of their work done and it sounds like the subject might be of interest. You may want to check it out.

Thanks for your question,
Ben Rubin & the AntAsk Team

The other day I was sitting outside my house with my friend. He and I were just sitting on the ground. There were a number of small black ants around us going about their business but not really in our way. After some time they began to fixate around the area I was sitting. They climbed on my feet and gave little nips and so on. After a while it got a little ridiculous so I moved to the other side of my friend where there were no ants at all. It was completely clear and not in (what I thought to be) their trail. It wouldn't have been more than five minutes later and then they were back again. They were all around me and the spot I had been in previously was completely clear. I just couldn't figure out what it was about me??? I should point out that my friend was left alone the entire time. It occurred to me later however that it had been "that time of month" for me and was wondering if they were reacting to the change of hormone levels?

Thanks for any help you can give me
CJ

Dear CJ,

I have never heard of ants being attracted to human hormones before but without doing an experiment, it would be difficult to say for sure what was happening. Ants would be more likely to respond to food smells. Were you carrying any food or had you been cooking recently? A sweet smelling perfume could also be attractive to ants. However, smells and insect responses to them are often unpredictable. For example, certain termites recognize pen ink chemicals as trail pheromones and can be tricked into following ink lines.

Thanks for your question,
Ben Rubin & the AntAsk Team

Dear Vidarshana,

This really is a great photo! Thanks for sending it to us! The darker ant in the center belongs to the genus Diacamma and the lighter ants surrounding and attacking it are members of the genus Oecophylla. The aggression between the ants may be the result of territoriality, predation, or a variety of other reasons.

Ben Rubin & the AntAsk Team

Hello,
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,

Max

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!
best,
Jesse Czekanski-Moir & the AntAsk Team

Hello,

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

Regards
Anna W
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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
Felicia
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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