Alex: Sure. The term refers to a particular form of society that is even more specialized than that of our own species. Instead of merely living together and interacting in groups, eusocial species have evolved to the point where most individuals have given up reproduction entirely, leaving procreation in the hands of one or a few highly fecund individuals.
Imagine a human city where only a few bloated individuals pop out all
the babies while everyone else keeps their head down and works the factories, tends the fields, and builds the roads. That’s what ants do. They’ve evolved separate reproductive castes and worker castes. Their specialization allows the worker caste to conduct their labor without the distraction of all the time and costs of courtship and reproduction, and allows the reproductive caste to be highly prolific.
Eusocial systems are very efficient. They are also fundamentally
different from social systems like our own, so I’d be cautious about drawing too many parallels.
Eusociality must have some advantages as it has evolved in many
disparate groups of animals. Many people know about the ants, the termites, the bees, and the wasps, but there are also eusocial shrimp, eusocial aphids, and a eusocial mammal, the naked mole rat of
DP: As social insects, ants are excellent communicators. How do ants "talk" to one another and how advanced is there communication?
Alex: That depends on what species of ant you are talking about. No one really knows how many species of ants there are, but we estimate that there might be around 20,000. Spread across that tremendous diversity are a great number of different ways to communicate, and a great variation in the extent to which social behavior and communication ability is developed.
Ants are predominantly chemical, “talking” with each other by what we would consider to be smell and taste. When an ant nest is attacked, for example, some ants will release a volatile chemical that acts as an alarm siren, priming their nestmates to be on the alert and to start acting aggressively.
Different ant species will use different chemicals to do this, produced in glands in different parts of the body. Most ants release their alarm pheromone from a gland in their mouth, but others use glands at the tip of the abdomen. One of my favorites is a group of pudgy little orange ants in the genus Lasius whose alarm pheromone is citronella. If you disturb a nest of these ants the air fills with a thick citronella odor. Some other species smell like blue cheese and others smell like feces.
Chemicals are also used to lay trails to food sources, to mark territories, to attract mates, and to regulate reproduction. Ants use chemical odors to tell if another ant is from their own colony or a different colony, as each ant colony has a specific odor. Some species can even tell what job a particular worker ant does by its odor.
One of the most striking behaviors of ant colonies is called trophallaxis, or liquid food sharing. Ants will feed each other continually, passing food among ants in much greater volumes than the individual ants need to survive. A constant flow of liquid among colony members helps spread chemical messages and helps to maintain the colony as a coherent unit.
Some ants are able to use sound to communicate. If a leafcutter ant is trapped, she will squeak until her nestmates come to her rescue. Ants also push and pull each other around.
DP: Is it true that ant colonies will attack one another and even capture enemy ants to use as slave labor? Please explain.
Alex: Yes, although this so-called “slave-raiding” is limited to a subset of species. The key to understanding this behavior is to grasp that young ants imprint on the colonies where they emerge from their cocoons. They think they belong to the nest where they were born.
Adult ants are rarely taken in raids, and the raiders normally target the immature ants, the larvae and the pupae. The captured pupae metamorphose into adult ants in the raider’s nest and imprint on
it. Once these captives begin working, they carry on as though they
were in the own nest. No one is holding them against their will.
Some species take “slaves” opportunistically and can survive without
them. But there are other species that have developed the behavior to the point where they are incapable of caring for themselves and have to raid other ant nests if their larvae are to be fed and their nests maintained. The genus Polyergus is the best known of these obligate parasites, they are bright red ants and they conduct spectacular raids on summer afternoons. In some respects it’s an easy way to make a living: let other ants expend all the energy working while you can skim off their labor and use it for your reproduction.
As the ant “slaves” do not recognize their condition, ant slavery is
not really comparable to human slavery and there has been recent discussion among myrmecologists (ant biologists) about adopting a different terminology less burdened with anthropocentric meaning.
DP: Other than humans and primates, ants seem to be the only creatures on earth that learn and teach. How do they do this?
Alex: Well, that’s still a contentious issue among researchers. Whether ants can teach each other is partly a function of the semantics of the word “teaching.” A study done in the
Is that teaching? Maybe. But I’m happy to leave this one for the
philosophers. I suspect the story that only ants and primates can
teach does a disservice to all those other species out there that have not yet been studied.