Evergreen Biota

Some common ants on the Evergreen State College campus.

Camponotus modoc: One of our more common carpenter ant species, and a common house pest in western Washington. These big bruisers can be seen foraging on the ground and on low vegetation, usually around the edges of clearings. They like to forage at night and are less often seen during the day. The workers really love sugar, and when they come into houses to forage on the kitchen scraps it is usually at night. Often workers found in houses are coming from nests that are outside in the woods. But if they are coming from a nest that is actually inside your house, well, too bad. Given enough time they can cause some structural damage, because they chew holes in wood to make a nest space. However, they don't actually eat your house the way termites do. Wood is not their food. So damage is usually quite local, and takes at least a few years to develop. Also, carpenter ants usually need some source of moisture around their nest site, so sound dry wood is not in danger. Face view (low res, high res); lateral view (low res, high res).

Formica obscuripes: These are the ants that build the big mounds of small sticks and conifer needles. They cannot sting but can spray formic acid, so when you handle them it feels (and tastes) like you have vinegar on your hand. They are very good at removing forest tree pests, and relatives in European forests are protected by law. On the down side, they can tend aphids and scale insects, and may cause an increase in these pests. Their thatch mounds are a unique miniature ecosystem that is home to many other species of tiny insects. Face view (low res, high res); lateral view (low res, high res).

Formica pacifica: These ants are very abundant in western Washington. They like open, highly exposed areas and are quick to colonize newly cleared ground. They were one of the first species to recolonize Mt. St. Helens after the eruption. They are common in parking lots, on sidewalks, and in not-too-lush lawns. They used to be common on the roof of the Evergreen Library (but may be having a hard time with the remodel). They nest in the soil. The nest entrances are inconspicuous holes in the ground, with a bit of excavated soil scattered around the entrance. Face view (low res, high res); lateral view (low res, high res).

Formica podzolica: This is like an all-black version of Formica pacifica. Formica podzolica is one of several very closely related species of all-black Formica, and I am never sure which is which. What I am calling Formica podzolica around here likes conditions that are a little less exposed than where F. pacifica is found. They nest in the ground but usually under stones or dead wood. They like grassy areas. Face view (low res, high res); lateral view (low res, high res).

Lasius pallitarsus: This little ant is extremely abundant in our forests. It is a real boreal ant, occurring across northern North America. Nests are mostly in and under rotten wood and they are most abundant in shaded forest. They are one of the few ants in our region that can live in such shaded conditions; most of our ant species require open areas. I often see the small yellow-brown workers foraging on low vegetation in the spring and summer months. Face view (low res, high res); lateral view (low res, high res).

Leptothorax muscorum: Now we are getting to the inconspicuous parts of the fauna. These are relatively common, but they are small and easily overlooked. The nests are in dead tree branches, rotten logs, and stumps, but usually in some part exposed to sun. The colonies are small, often with fewer than 100 workers. The workers usually go out to forage alone, so you don't see columns or aggregations of workers. If you find a big log lying in the sun, at the stage of decay where the bark has fallen off but the wood surface is still hard with lots of little holes, you can often see many of these little ants scattered over the surface. Face view (low res, high res); lateral view (low res, high res).

Myrmica incompleta: This is a member of a genus that has several species in our area, but it is difficult to tell species apart and the names for them are not well worked out. These ants nest in the ground and like open areas. The colonies are small and you never see a lot of them together. If you get your nose down to the ground on a sunny day in a lawn with open bare patches, you may see workers of these walking around. Face view (low res, high res); lateral view (low res, high res).

Stenamma diecki: These are wonderful ants because their knowledge to abundance ratio is so low. They are very abundant in leaf litter on the forest floor, but in spite of their abundance are rarely seen. They have small colonies, often only a few dozen workers, and the nests are deep under large stones. The workers have very small eyes, indicative of their life foraging in and under the leaf litter rather than on the surface. You won't find these at your picnic, and you won't necessarily find them if you go look in the leaf litter of the forest. They walk very slowly, and if they are disturbed they curl up and remain motionless, which makes it rather difficult to see a 2mm long ant. But if you take a bunch of litter and spread it out on a sheet and wait around for a while, you may see them gradually start to move. But quantitative samples of leaf litter from which the arthropods are extracted reveal them to be one of the most abundant ants in the forest. Our forest understory, in the shaded areas, are dominated by two species: Stenamma diecki and Lasius pallitarsus. Face view (low res, high res); lateral view (low res, high res).

Tapinoma sessile: These are the little black ants that come into your kitchen in early spring, wandering around on the countertops and looking for sugar. They are too small to be carpenter ants. Tapinoma sessile is an extremely generalized species that can be found in all the 48 contiguous United States. It loves to nest in open sunny areas under debris on the ground. Colonies can be large, with thousands of workers. They can be in almost any habitat, from sea-level to the high mountains, as long as there is some exposed ground that gets full sun. And for some reason they are common in and around houses. They don't do any damage and they can't really rob enough sugar from your kitchen to affect the family budget, so they are the kind of ants that are best observed closely for the educational value rather than exterminated. Face view (low res, high res); lateral view (low res, high res).

Solenopsis molesta: These are our own local relatives of the notorious fire ants from further south. But in contrast to those, who could probably run for public office given their celebrity, here they couldn't be any less conspicuous. The group of species that includes S. molesta are called "thief ants." They are extremely tiny, a little bit more than a millimeter long, and are never seen above ground. They are most often found when you lift a rock, find the nest of some larger ant species, and the little Solenopsis will be in tunnels and galleries under the same rock. Although there isn't much evidence, it is thought that they may often be thieves, nesting near other ants and sneaking into their chambers to steal food and perhaps the eggs and larvae. Face view (low res, high res); lateral view (low res, high res).

Page authors: John T. Longino and Casey Richart longinoj@evergreen.edu
Last modified: 11 April 2003