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the new facial pattern of their nest mate. It was clear that the wasps were not simply reclassifying the painted females into rough categories, such as "familiar" or "unfamiliar," because paper wasps use chemicals on their outer surface for that purpose; furthermore, a female perceived to be from outside the colony would have been ripped to shreds or chased away, not simply pushed around a bit more than before. What is more, the wasps didn't seem to care how the apparent interlopers were painted—a bit more yellow on the chin garnered no more or fewer attacks than a larger brown stripe between the eyes. That means that the wasps are not using the face patterns as an indicator of size or age or some other quality of an individual, but instead as genuine identity tags; having two black spots, for example, doesn't say, "Stay away from me, I am large and fierce," but rather, "Sam I am" (or Samantha, in this case).

In another species of paper wasp, P. dominulus, facial patterns do indicate both size and dominance, and females pay particular attention to the blotchiness of the black marks. A more broken pattern means a robust, higher-quality individual, for reasons that aren't yet clear. This time, Tibbetts painted the faces of the females so as to either make them look more or less dominant, and then allowed the wasps to guard a sugar cube in the lab; in the wild, the wasps eat nectar, but they happily consume sugar in captivity. Pairs of wasps, one painted to look like a subordinate and one to look like a dominant individual, were each assigned their own sugar cube, and then another wasp was introduced to the container. The wasps share food, but dominant individuals are harder to coax into contributing than submissive ones. As you might expect, the supplicating wasp was more likely to choose a cube being defended by a wasp whose facial pattern suggested she was a loser. What's more, when Tibbetts staged encounters between wasps that were strangers to each other, a subordinate individual painted to look like a dominant one was much more likely to be beaten up by the real dominant wasp, showing that even wasps dislike a cheater. Interestingly, other researchers studying the same species of wasp found that body size, rather than pattern, was important in determining social rank in a population from Italy (Tibbetts works in North America); the reasons for the difference are not well understood but may have something to do with the timing of food shortages and, hence, growth of the young insects.

It turns out that individual recognition is more likely to evolve in wasp species that show more complex social behavior than in those with more short-lived or simple interactions. In some species of paper wasps, a single female always starts a nest, and her daughters then contribute to the growth of the colony. In others, several females build the cells and attempt to lay their eggs simultaneously, giving rise to the jockeying for social status described above. Among yet a third group, either approach is seen. Each of these scenarios calls for an increasingly astute approach to social politics. As one might expect, species that are likely to have complicated group dynamics, as indicated by the likelihood that multiple individuals will have to work out their hierarchy, are more likely to show a lot of variability in their markings.

What about Wart's ants? Contrary to his experiences, they too can recognize individuals, although unlike the wasps, they lack the distinctive facial or other body patterns used to tell one six-legged companion from another. Instead, ants use chemical signatures, individual odors that ants produce on their external skeletons. We have known for a long time that ants as well as many other insects use such chemicals as general news bulletins—"I am one of you; let me through," or "Female here, sexually available till six"—but had always assumed that such rough categories of signals were the limit of their abilities. But Patrizia D'Ettorre from the University of Copenhagen in Denmark and her colleagues wondered whether