Summer flings: firefly courtship, sex, and death.

Publication: Natural History

Publication Date: 01-JUL-03

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COPYRIGHT 2003 Natural History Magazine, Inc.

The fireflies, twinkling among leaves,/make the stars wonder. --Rabindranath Tagore (1861-1941)

As light slips from the summer sky, an army of male fireflies awakens from its daytime slumber. One by one, the insects march up blades of grass, waiting until dusk to lift off like miniature helicopters into the night. Yet these fliers aren't bent on military conquest; their goal is simple evolutionary survival. The fireflies we study--bioluminescent members of the genus Photinus--devote every night of their short adult lives to courtship, first broadcasting their amorous intentions with flashing light signals, then seeking to mate with responding females.

Few insects are considered charismatic, but fireflies are a clear exception. All over the world their spectacular courtship displays have long delighted children and inspired poets. On long summer evenings throughout the United States countless children chase fireflies through fields and backyards. In Japan, where a broad respect for nature is both traditional and deeply felt, fireflies--hotaru--are particularly revered. School graduation ceremonies feature the song "Hotaru no Hikari," which means "fireflies' light," and many cities celebrate communal firefly watching with annual festivals known as hotaru matsuri ("fireflies' festival"). In the popular Japanese cartoon Sailor Moon, the heroine is Tomoe Hotaru, a name that means "firefly of earth." And in Japanese poetry the firefly serves as a metaphor for silent yet passionate love.

As biologists, the two of us still fall under the spell of fireflies. In particular, it is their single-minded focus on procreation that has inspired us, as students of the evolutionary process of sexual selection, to spend countless nights for the past several decades observing their drama of love and death. We, along with our colleagues, have been keen to learn what makes certain individual fireflies more likely than others to find mates and insure that their genes are passed on to future generations. And our observations, both in the wild and in the laboratory, have led to new insights into how fireflies (and other species as well) play the game of evolutionary survival--how they live, love, and die.

Fireflies are not flies at all, but beetles, belonging to the family Lampyridae. To date, entomologists have formally described some 2,000 firefly species worldwide. The family includes some non-luminescent (and often diurnal) species that rely on pheromones to locate mates, as well as some species that merely glow rather than flash. In North America the flashing fireflies fall into three main genera: Photinus, Photuris, and Pyractomena.

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