Carpenter Ants

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Carpenter Ants on Alder Creek Trail

I'm thinking about ants this morning for whatever reason, but these handsome fellows with their bejewelled butts are definitely worth of thinking about. These guys in the picture are carpenter ants (Camponotus). I don't know my ants, but they are perhaps the common C. modoc given the red legs (the banded abdomen seems distinctive, but I don't know). Unlike termites, they don't eat wood. "Carpenter ants are voracious predators of arthropods, such as flies, caterpillars, beetles, harvestmen (daddy long-legs), and spiders. Carpenter ants also collect honeydew from aphids and can often be observed tending them."[3]

The queen starts by herself and raises her first brood of semi-undernourished minors, little workers that don't get very big because the queen has to raise them herself from reserves within her own body. They then tend to the next crop of carpenter ants, which will get bigger (called majors or soliders) because of the better nutrition. It takes the queen and her minors about two to four years to build the colony up to 200 to 300 ants. A colony will take six to ten years to reach 2,000 workers. Eventually a colony can have 10,000 to 100,000 workers, often connecting "parent" colonies with satellite colonies by way of well-maintained trails[1].

The queens of C. laevigatus, also common in the Sierra Nevada, are known to have lived as much as 27 years. Simple workers can live for several years[2].

In winter, they go into "diapause", a state of dormancy where, among other things they produce glycerol (effectively, anti-freeze) to keep themselves from being damaged by freezing temperatures over the winter.

In the spring of 2011, I got to watch two colonies of ants battling it out in Yosemite Valley near Cook's Meadow. It looked like a colony from one fallen log and a colony from another had each set out to forage or whatever, and encountered each other on the open field of glory, otherwise known as the bike path. These battles can be waged across a front 90m long and go on for days, leaving a carnage of thousands [3]. Our hapless ants were no doubt confused by wanton destruction of the nuclear weapons of the other side, coming in the form of early-morning bicyclists who, taking no sides, rolled over plenty of ants. So in addition to dismembering each other and leaving body parts by the hundreds, a fair number were also crushed to cellular ooze.

Despite their warfaring ways, carpenter ants do not behave like army ants and get locked into circular mills or death spirals. Army ants will sometimes split off from the main group, start going in a circle and rejoin the column, which means the trail is then circular and they will march in that circle until they die of, for example, dehydration. Army ants are sightless and their foraging strategy depends on large swarms foraging together. Carpenter ants are way smarter, individual foragers. Researchers have marked carpenter ants out at their foraging grounds and carried them back to the home tree only to find them foraging in the same place the next day[3]. Because of this, they're not susceptible to getting caught in a death spiral like army ants[4].

One other interesting aspect of their foraging is that, as colonies get really big, their energy needs get really big and the ants need to forage farther and farther afield. This means that they need higher and higher quality food sources to maintain population or grow. With a small colony, ants need not travel far to forage, so if the food doesn't provide a huge amount of energy, that's okay. It doesn't take a lot of energy to obtain it. But once an ant is starting to travel a long ways, he needs to find really good food so that the energy required to go out and gather the food is less than is returned by what he finds.

Sources

  1. Carpenter Ants: Their Biology and Control (Extension Bulletin 0818), Washington State University Extension Serrvice (download pdf).
  2. http://www.calacademy.org/exhibits/ants/#carpenter
  3. Carpenter Ants, by John H. Klotz, Laurel D. Hansen, Byron L. Reid and Stephen A. Klotz, The Kansas School Naturalist, Volume 45, Number 4 (July 1999).
  4. T.C. Schneirla, "A unique case of circular milling in ants, considered in relation to trail following and the general problem of orientation," American Museum Novitiates, number 1253 (April 8, 1944). The classic paper on circular mills. See p.22 on carpenter ants.

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