November 2012 Archives

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

Ectoparasitic mites on ants


Hello AntBlog team,

I have a few questions and I was wondering if you could help me?

I recently acquired a small colony of Camponotus morosus, I housed the colony inside an aerated autoclaved concrete nest, however just after the colony had moved in I was taking photos and noticed what appear to be very large (In ant terms) mites, I have only noticed 2 of the mites in the colony so far, the thing is I cannot manually remove the mites unless the workers come out to forage with them on as the nest is affixed to the inside of a glass tank.

Strangely the mites only seem to attach to the very small minor workers who do not leave the nest to forage, they are mobile and I have seen them moving from one ant to another and they always latch on the underside of the ant, they do seem to bother the worker they latch on to.

I was wondering if you could give me any information on these mites as they are unlike any ant associated mites I have come across before.

How can I get rid of them? Are they parasitic or phoretic? Will they hurt my colony?

And finally if you have any information on C. morosus you could give me I would really appreciate it, I'm afraid I have not been able to find a lot of information out on the internet as of yet!

Regards,
~Daniel
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Dear Daniel,

Wow! Those mites are really amazing! We contacted a colleague, Kaitlin U. Campbell, who is an expert in mites found on ants to see what she had to say:

"Dear Daniel,

Thanks for sending the great pictures of these exciting mites you found! As you might imagine mites are pretty difficult to identify from images, and the specimens typically must be mounted on microscope slides to get accurate identifications. You are correct about these being very large mites (in terms of ants on mites). There are very few people working on mites associated with South American ants that aren't army ants, and to my knowledge none of them have looked at Camponotus. If this mite is truly associated with Camponotus morosus and not just there by accident, it is likely a new species. The best identification I can give you from these pictures is that it is in the Mesostigmata. Unfortunately this doesn't provide much information in terms of what they are doing. Here is a summary we do know about ant associated mites:

The majority of ant associated mites typically fall into 3 subgroups of mites: Mesostigmata, Heterostigmata, and Astigmata. All of these groups have members that ride on the ants (phoresy). Astigmata and Heterostigmata are typically smaller in size than the Mesostigmata. The Astigmata and Heterostigmata that I have encountered are generally believed to be fungivores or bacterivores taking advantage of the resources inside the ant nests, and possibly cleaning up when they are not riding on the ants. There are only a few genera of Heterostigmata that are known parasites. Because of their mouth parts and what little we know of their ecology, we believe these two groups are the least likely to cause any harm to the ants. In fact the phoretic Astigmata (their Deutonymph stage) do not even have mouths and only get mouths when they develop to the next stage after the disembark from the host!

The Mesostigmata, however, are a different story. Many of these have large enough mouth parts that they could actually cause damage to the hosts. The majority of the "mesostigs" are still thought to just use the host to get around (they are probably predators of other mites, Collembola, and nematodes or scavenging in the nests), but a few are known to pierce the hosts' cuticles or feed on brood. As you can image, mite behavior is difficult to study, so few have actually looked into this in detail. The most well studied Mesostigs are either associates of Army ants (many of which have really unusual body shapes), Macrodinychus species parasitizing developing brood, or Antennophorus species a cleptoparasite (steals food) on Lasius ants. What you have is not any of these! Yours looks most similar to the Antennophorus species, and may be in the same Suborder, but without having the specimen on a slide it's not going to be possible to tell.

Concerning whether they are bad for your colony- As I mentioned before, very few mites are known to actually cause damage to their ant hosts. I am suspicious of your mites, however, because of their orientation on the ants. They seem to be positioned in areas with their heads near soft tissue, and you said they do seem to bother the ants. The ants could just be bothered because the mites are large and cumbersome to be carrying around, though. They could potentially be harming the ants, and you should monitor the mites behavior and the health of your ants. It's very difficult to get rid of mites on the ants without harming the ants with any chemicals. Since you only have a couple it would be best to just remove them individually from the ants if you can ever get the small ants to exit the nest area. If they are seriously harming the colony, your only option may be to open the nest and remove the ants carrying the mites. I would just watch them closely and resort to active removal if they seem to cause a lot of damage.

If you are able to remove the mites and interested in knowing what they are (I sure am!), please preserve them in ethanol and send them to me and/or take individual pictures of the dorsal and ventral sides of the mites.

This is a cool find, and I'll be interested to hear more! I hope this helped!"

Best regards,
Kaitlin U. Campbell (guest expert), Corrie Moreau & the AntAsk Team

Hi:

Looking at tiny bugs, I have always wondered whether big ones, having much bigger brains or at least room for them, are "smarter" than small ones.

In answer to a question about the largest ant, you mention some that are 3 cm long, compared to the smallest that are <1mm. That is a length ratio of 30 times, which means mass and volume differ by 30^ 3 = 27,000 times. This is consonant with what you imagine, looking at a barely visible member of the phylum we kids called "piss ants" (which I'm sure is the Latin technical term!)

A 3 cm ant is like a roach or other bug and you don't expect it to be very smart, but it probably does have a large hard-wired repertoire of behaviors -- forage, fight, mate etc. But at 1 mm, brain shrunk 27,000 times, you have to wonder whether there are enough neurons to code for all that. Is there some limiting size beyond which bugs get dumber? I recall from high school biology fifty years ago that bugs probably don't have brains per se, but several ganglions (ganglia?), and most of the cells therein are used to drive muscles, so it's proportional and a small ant needs only a small ganglion for that. But for seeing and behavior and the like there must be a minimum number of neurons required.

So -- how tiny can they be before they start to get dumber?

Alan
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Dear Alan,

To address your question about ant brains, we contacted one of your colleagues who is an expert on ant brains, Dr. James Traniello, and here is what he had to say:

"First of all, insects do have well-structured brains made of compartments of tissues with specialized functions in visual and odor information processing, motor control, and learning and memory! Only a small portion of the brain (and ganglia) appear to control muscles.

It's been a great challenge to understand the relationship between the structure and function of the brain and whether or not small size compromises processing ability and "intelligence." It's been assumed, particularly in vertebrates, that brain size and cognitive ability go hand-in-hand, but animals with larger brains are not necessarily "smarter." There is no question that tiny insect brains can generate complex behavior (In this respect, Charles Darwin thought the ant brain was more marvelous than the human brain). It's an open question as to how many neurons are needed to generate complex behavior. Some models suggest very few nerve cells are required for learning, for example.

Social life and ecology affect the evolution of brain size; body size alone does not appear to be a very good predictor of cognitive ability. Larger worker ants don't appear to be any "smarter" than small workers and any differences in behavior, especially learning and memory, are likely due to differences in their foraging ecology rather than their size per se. Larger ants may, for example, hunt for prey and have better vision, and this ability is reflected in the size of the optic lobes of the brain that process prey stimuli. Small ants may have relatively large brains, and different ant species have brain compartment proportions that fit their ecology and behavior.

It's also important to remember that ants are collectively intelligent: they solve problems as communicating groups. How this group intelligence affects brain evolution is not well understood. Ants with large colonies may have workers with relatively smaller brains. The smallest bodied ants may have fewer cognitive abilities as individual workers, but their colonies may be just as "smart" as colonies of ant species that have larger body size. "Intelligence" has to be considered in respect to ecology, social behavior and life history in all animals."

To see an image of an ant brain, please see the home page of Dr. Traniello's lab website: http://people.bu.edu/jftlab/Home.html

Best regards,
James Traniello (guest expert), Corrie Moreau, & 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

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.

Thanks,
Maria
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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.

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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.