Ants are everywhere. There are about 12,000 described species of ants, and taxonomists think there are probably about 20,000 species total. This is a pretty substantial adaptive radiation, so obviously there is something about the ant "adaptive syndrome" that is quite successful phylogenetically. Systematists are of the opinion that ants evolved from wasps, and they are unified by a number of synapomorphies. For instance, all ants are eusocial, which means they have cooperative brood care, reproductive division of labor, and overlap of generations. Ants have a queen and workers who live together in a colony; the workers are the daughters of the queen; they care for the brood, which are the offspring of the queen and the sisters of the workers. Ants as eusocial insects have a caste system, although the workers of many ants are monomorphic, and few ant species have evolved specialized soldier castes. The most common castes in ants are the primary reproductives, the secondary reproductives or alates, and the workers. Ant colonies may have a single primary queen (monogyny) or multiple primary queens (polygyny). The fire ants around here are polygynous, and the seed-harvesters are monogynous.

Ants have a variety of ways of making a living, including predation (the army ants are voracious predators), gardening (the leaf-cutter ants raise fungi that they feed on), and seed-harvesting. Ants are extremely important components of many ecological communities. In some tropical areas, there is more ant biomass per hectare than there is biomass of vertebrates. Ants are important processors of biological material in the ecosystem and alter the soil through their digging activities. Ants have evolved "mutualism" with a variety of plant species, where the plants provide a place for the ants to live and in some cases food, and in return the ants provide the plant protection from herbivores. Ants are also important food sources for some animals, including lizards, some snakes, some mammals, and sometimes other ants. Of course, ants have a good way of protecting themselves from predators. All ants sting, and some have powerful and painful stings. It is the workers who sting; the sting apparatus is a modified ovipositor which only females have.

The local species of seed-harvester ant is Pogonomyrmex barbatus, which are known in the business as "pogos", and which I grew up calling "red ants". This is the ant that makes the large mound or crater around the entrance to its nest. The craters around here consist of small pieces of rock which are bitten out of the bedrock to make the tunnels of the nest. One possible function of the crater is as a heat source, to help warm the upper regions of the colony; the small stones absorb solar heat and transmit it into the ground. Also surrounding the entrance is the refuse pile (for seed husks, dead prey parts, and the bodies of the living workers' dead sisters). Pogo colonies are usually large (up to 30 000 workers) and deep (10 m in soft soil), and are generally haplometrotic and monogynous. The colonies are perennial and long-lived; the reported life-span of the queens of congeners P. badius and P. owyheei are 17 and 30 years (!!) respectively.

Pogonomyrmex barbatus workers are monomorphic and are about 6 mm long. They have a powerful sting but do not mob before stinging as do fire ants. They forage in what are called "trunk trails", which means that many workers leave the colony and go out in a particular direction for a considerable distance before fanning out in search of food. The trunk trail is marked by pheromones, but is often visible near the crater because the ants remove vegetation and other obstacles to make their travel easier. You can see their little autobahns running away from the crater. A trunk trail can be recognized by the constant stream of ants running back and forth, although the number of foragers decreases as the distance from the colony increases. Trunk trails of 15 m or more in length are typical. I have seen trunk trails 65 m in length (this is approximately equivalent to a 5.5 ft human running 11 miles and back to the grocery store). Trunk trails are a persistent feature of the topography around ant mounds; they last for months or even years. The foragers pick up seeds but also any animal matter that they find and can clip apart and carry back. The mass of the object that a worker carries does not seem to affect the velocity with which she can run. Often workers will carry objects equal in mass to their own.