Anyone who has ever lived in an older home knows what it's like to live alongside uninvited guests. Sowbugs, silverfish, and spiders, while annoying and messy, are relatively benign. Ants are a more serious problem, requiring a bit of technique if elimination is your desire.
We've had carpenter ants as long as we've lived here. As their name suggests, they can cause structural damage to a home as they use their powerful mandibles to cut away wood to build their nests. They are easily identifiable by a combination of their large size, and a single node, or hump, between their thorax and abdomen. You can see this node in the image above, below the wings, right behind where the final pair of legs is attached to the thorax.
Carpenter ants are among the largest ants that you'd see in our part of the world. Fortunately, they lack stingers that their smaller cousins the fire ants readily deploy, but their mandibles are quite capable of giving you a bit of a nip should you decide to hold on to one. As a larger ant, examining the anatomy is quite easy. You can quite easily see two of the three ocelli (single eyes) at the top of the ant's head in the image above. They are so positioned to enable the ant to detect changes in light levels overhead.
To eradicate ants, one must remove or kill the queen. Because the nest is hidden in the wall, doing so mechanically is impossible. The queen rarely strays away from the nest once it is established, so the most effective technique I've found is to use ant poison, a syrupy mix of sugars and borox. The worker and soldier ants readily slurp this up and deliver it to the queen, and within a week of administering the poison (replenishing it as it is consumed), we would no longer see any signs of infestation. However, pupae do take up to two months to develop, so while the workers have all died off, it is still possible that within a few weeks they will seem to return.
This particular queen was one I found just walking around in our hallway. In the social structures of ant and bee colonies, the pupae (nearly all female) develop into workers and soldiers. The existing queen's pheromones suppress the development of these pupae into queens. Possibly what happened in our case was that the queen had succumbed to the poison, and the existing pupae were blossoming into queens which would then seek out new nesting sites (and males). Instead, this unfortunate queen found me.
I'm much too respectful of monarchy to kill a queen ant, but I'm not above using her life to benefit a creature that I appreciate a little more than an ant.