shooting the frass

As a not particularly attractive job description, evolutionary faecologist would probably rank right up there with, oh, just regular old faecologist. But the often-ignored study of excrement can lead to strange discoveries. For example, the skipper caterpillar can shoot its feces — known as frass — more than 5 feet away, a phenomenal distance — on a caterpillar scale. Why would an animal evolve such a bizarre talent? Biologist Martha Weiss of Georgetown University addresses this question in the April issue of Ecology Letters. The caterpillars construct shelters out of the leaves of their host plants, and forcefully eject their feces great distances away from where they live. Weiss tested a variety of hypotheses, from hygiene to space preservation within the shelter, but found that being surrounded by great quantities of frass didn’t seem to have much effect on the health of the caterpillars. What Weiss did find, however, is that excrement attracted predators. Caterpillars whose shelters were decorated with frass were easily found and eaten, whereas the caterpillars that ejected their excrement remained relatively untouched. (And please, kids, don’t try this at home.)

This news brief appeared in the Random Data column of the Boston Globe’s Health/Science section on 4/01/2003.