LED Lights Help Scientists Demystify Firefly Sex

For fireflies, size does matter—that is, the size of a spermatophore: a “package containing sperm and nourishment for the female,” which a male delivers to his lover once physical contact has been made. We should all be so lucky.

Biologists Adam South and Sara Lewis from Tufts University discovered this previously unknown detail of firefly courtship while using LED lights to mimic the insects’ highly luminous mating ritual. They discovered that while the males’ flashing light displays are important for initially attracting a mate (the females only flash back to males whose light patterns they find attractive), the size and transfer of this beneficial “package” is what seals the deal. In the first part of the study, scientists used small, dimmable LED lights to replicate male firefly flashes (both attractive and unattractive) for an audience of female fireflies. Then they placed both male and female flies in a small container and recorded the proceedings under infrared LED strips. There, researchers witnessed female fireflies choosing males based on the size of their spermatophore, not on the patterns of their light display, as previously thought. “Attractive flashes only seem to benefit males during the early stages of firefly courtship. Initially, flashes are important,” he explained. “[But] once males make physical contact, females switch to [this] alternative cue.”

Maybe fireflies aren’t so different from humans after all—a nice looking partner may attract us from the start, but in the long run, we’d much prefer one who can bring home the occasional bag of groceries.

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