Fireflies Fatales

As conniving femmes fat ales, Mata Hari and Delilah pale by comparison to female fireflies of the genus Photuris. Like other fireflies, these nocturnal, winged beetles send out short, rhythmic flashes of light as part of a special signal system that attracts males of the same species. The female Photuris practices a deadly variation of this ritual. It modifies its signal to mimic the flash pattern of different species of fireflies and thus lures unsuspecting males. Once they are in reach, the female devours them.

This odd bit of insect behavior was discovered by James E. Lloyd, an entomologist at the University of Florida in Gainesville. While studying fireflies on the ground or in low vegetation in the university's biological preserve at Gainesville, Lloyd watched male fireflies on the wing emitting light signals. These varied in number, rate and duration from one species to another, as did the responses of the females perched on shrubbery below. Using a pocket flashlight, Lloyd learned to imitate the signals of various species. He soon discovered that when he gave the mating flash of a male Photinus, a female Photuris sometimes responded. When Lloyd switched signals, flashing the mating pattern of a different male species, the versatile female Photuris often began to mimic the proper response for the female of that species. In fact, a female can mimic the signals of at least three different species.

Locomotion Flashes. Lloyd believes that the mimicry is not always perfect; male fireflies--apparently noting slight differences in the flashes and suspecting female wiles--are not always taken in by the ruse. But the female Photuris generally manages to lure, capture and swallow at least one male out of every ten for whom she sets her cap.

How did such mimicry evolve?

Lloyd noted that the females' responses to certain Photuris males are similar to the flashes the females give off when they walk, land or take flight. Perhaps these "locomotion" flashes were gradually modified to attract males of different species. In any event, the Photuris' wide range of mimicry suggests to Lloyd that the lowly firefly has a more complex brain than entomologists ever suspected.

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