December 2012 Archives

From: Nancy
Subject: Thatch ants Washington State

We have a red-headed thatch ant colony more than six feet across near
large fir, cedar and big leaf maples. I am told variously that these
ants are beneficials, do not damage homes, are only moderately keeping
of aphids on ornamentals, and while they can bite if provoked, are
not dangerous. All this being said, my question is: Do they in any
way damage the trees, particularly the conifers, adjacent to their
nest? I would prefer to take the live-and-let-live approach and leave
them to enjoy their metropolis. We enjoy watching them and will leave
them alone if they aren't damaging the structure of the very large
trees near their mound.

Thank you in advance for your help.

Dear Nancy:

Thank you for your message to the ant blog. It sounds indeed like the ants you describe are the famous thatching ant, Formica obscuripes. The species abounds in some parts of the western conifer forests, and curiously, also extends south to the sagebrush plains of New Mexico and east to the prairies and old fields of Wisconsin and Michigan! Though it does befriend aphids, this may be considered the plant-to-ant equivalent of the cost of feeding a standing army. F. obscuripes is considered a beneficial insect over all, because of its prodigious predation of plant-eating insects, including such pests as spruce budworm. We applaud your live-and-let-live attitude, and are very pleased you chose to ask before acting.

Best regards,

James C. Trager of the Ask Ant Team

Hi there,

I live in Vancouver, Canada, and am wanting to establish an army ant farm. Can you suggest how best to go about this?


Dear Paul,

Starting an army ant farm in Vancouver, Canada could be very difficult for a number of reasons. First off, by nature, army ants are inherently nomadic predators, and thus keeping them in a confined space such as an indoor "farm" might be next to impossible if you want them to last very long. Secondly, most of the 5 genera of New World army ants (Cheliomyrmex, Neivamyrmex, Nomamyrmex, Labidus, and Eciton) are primarily Neotropical. While some species of Neivamyrmex have been seen as far north as Iowa (see this helpful ant distribution website), Vancouver is still hundreds of miles farther north, and with the cold humidity, it is doubtful any species of army ant could survive. Those that could for a short period would probably be subterranean, and you would need quite an arena to visualize and house a colony of thousands to millions of nomadic predators.

However, in 2005, Dr. Brian Fisher--myrmecologist extraordinaire--was able to import a colony of Eciton burchellii army ants to the California Academy of Sciences for the exhibit "Ants: Hidden Worlds Revealed". The advantage of importing Eciton burchellii in comparison to the many other army ant species is that they're generalists--they'll eat just about anything. The downside is that the millions of workers need a lot of space and have quite an appetite. Dr. Fisher informed me that Cal Academy was feeding the colony over 25,000 crickets a day, which they let loose in a giant chamber housing the colony in the museum.

Thus, unless you have the resources to build an arena and find the appropriate diet (smaller colonies will have more restricted diets--such as ant, wasp, or bee larvae), it might be a difficult task.


Max Winston and 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 32ÂșC, 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

Hi AntAsk,

What specific dates (time frame) do harvester ants have to gather their food before winter strikes?


Dear Javier,

Thank you very much for your great question. We have contacted Christina Kwapich, who has done some great work on harvester ants, to address your query. Here is what she had to say:

"While there are numerous genera and species of seed harvesting ants, none is more charming (or easier to exhume) than the Florida harvester ant (Pogonomyrmex badius). Populations of P. badius dapple the coastal plain, east of the Mississippi river and favor spots with well drained, sandy soil. Between March and November of each year foragers seek out seeds, insect protein and even freshly cut slivers of fungus to feed crops of hungry larvae. Seeds are the only physical products that colonies store over winter and some colonies really know how to fill the pantry! Walter Tschinkel noted that one large P. badius colony housed over one pound of seeds (Tschinkel 1999). While we don't yet know how long the oldest seeds remain in P. badius seed caches, Preliminary data from the Tschinkel lab show that fresh seeds are frequently processed within days of collection, while some apparently 'uncrackable' seeds linger indefinitely. This means that the old "first in first out" adage may not apply when it comes to stocking the shelves in an ant nest.

Although numerous chambers brim with seeds all winter long, adults don't appear to ingest a morsel of the spoils. It might be tempting to exalt them for their willpower, but the truth is that the narrow waists of adult ants prevent them from ingesting solid food. In fact, seeds and other solid food items are collected expressly for consumption by hungry larvae; which only appear from April to November of each year. In the absence of a liquid diet, adult P. badius workers rely on ample fat reserves to tide them over the winter months. The age of adults entering the over-wintering period ranges from 10 to 60 days, but whether or not these individuals consume a special diet in preparation for the long stretch is unknown (Kwapich and Tschinkel, unpublished). We do know that when winter begins, workers enter a period of reduced activity, abandoning their posts across many meters of vertical nest space to occupy only the bottom-most chambers (a cozy 24 degrees Celsius, all year round, i.e., 75 degrees Fahrenheit).

The presence of winter seed caches may lead one to believe that seeds play a key role in springtime alate (those are the winged sexuals in ants that form the next generation) and worker production. Surprisingly, Chris Smith (2007) demonstrated that when prevented from foraging, colonies did not tap into their ample seed reserves and use them as a buffer against starvation. Instead, it appears that spring-time worker fat-reserves (garnered in autumn) are most important to the production of alates and new workers following winter. So, to answer the original question, it appears that P. badius workers spend nine months adding and subtracting from a large seed cache which may be of no critical importance at all! This should not be entirely befuddling, as Willard and Crowell (1965) noted that another seed harvester, Pogonomyrmex owyheei, successfully enters and exits winter without stored products of any kind."

All the best,
Christina Kwapich (guest expert), Steffi Kautz & the AntAsk Team

P. badius chamber.jpg

This photo shows a half-filled Pogonomyrmex badius seed chamber. Photo by Christina Kwapich.

Works cited:

Smith, C. R. (2007). Energy use and allocation in the Florida harvester ant, Pogonomyrmex badius: are stored seeds a buffer? Behavioral Ecology and Sociobiology 61:1479-1487.

Tschinkel, W. R. (1999). Sociometry and sociogenesis of colony-level attributes of the Florida harvester ant (Hymenoptera: Formicidae). Annals of the Entomological Society of America 92: 80-89.

Willard, J. R. & H. H. Crowell (1965). Biological Activities of the Harvester Ant, Pogonomyrmex owyheei, in Central Oregon. Journal of Economic Entomology 58:3.