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said to have this form of the disorder. Prosopagnosia can also be present to greater or lesser degrees, so that one can have the disorder under certain circumstances but not others. In severe cases, sufferers cannot recognize their own face in a photograph. It seems to be related to the inability to navigate in the environment, which means that bees might be particularly suitable for using as models for studying the disorder, since of course bees are superstars at locating food sources and remembering nest sites. At the moment, no one has worked out the mechanisms by which the bees learn faces, but if they are linked to the ways in which the bees orient in the wild, understanding the bees' abilities could help people overcome their own face blindness.

Each Ant, Teach Ant

WE—AND other animals—can learn things from objects in the world around us, like Dyer's bees or the wasps that remember the location of a rock near their nest. But most of us remember learning in school, from teachers. Insects may lack classrooms and textbooks, but increasing evidence suggests that they too can learn from, and act as, teachers.

In common use, the word teaching usually means the transfer of information from one individual to another. A boy sees his sister feed the dog under the table and promptly learns to get rid of his unwanted broccoli the same way. Under that definition, though, even casual observation of another animal doing something that the observer then does would qualify. You could learn to run away from fires by noting a crowd fleeing a burning building, for instance, but has the crowd actually taught you? Even Charles Darwin suggested that many animals, including insects, do this; bees, he pointed out, could follow another worker flying to a source of nectar. If crickets are placed in a container with other crickets that have been hiding under leaves from predatory spiders, they are more likely to find a shelter and hide themselves. But this kind of use of public information seems a bit too haphazard to be real teaching. Animal psychologists are more stringent in their definition and often require the behavior to happen only when a naive observer (one that doesn't know how to do the task being taught) is present. That means that although a young male white-crowned sparrow learns his song from his father, the father isn't teaching him, because the adult bird would sing whether or not his son were there. Teaching also has to help the observer while costing the teacher something, usually the time and effort required for the demonstration.

Finding an occurrence of this more narrowly defined behavior in nature has been daunting, and until very recently scientists had essentially no examples of real teaching by animals. Just within the last few years, however, researchers have found three cases of it—one in a bird, one in a mammal (the meerkat), and one, in credibly, in ants. People are often surprised by the selectivity of this group, suggesting that surely some other primate besides humans teaches in a natural setting. At least for the moment, the answer appears to be no, which says something about our anthropocentric desire to only see, or bestow, special qualities on those we think are closest to us. That teaching happens in ants and not monkeys or apes is unsettling for the same reason I love studying insects: it's all about getting to the same destination with different modes of transportation.

As anyone who has had to battle the brown ribbons of workers heading toward the sugar bowl knows, ants follow each other to get to food sources. It looks like they are just marching endlessly, one after the other, perhaps following the smell left behind by earlier foragers, but paying no more attention to each other than riders on the same subway train. Odor does play an important role in leading ants to food. But in at least one ant species, a single worker will actively recruit another ant to follow her to a food source or a new nest, or just to explore a new area, in a process called tandem running. The lead ant goes in front,