Why Do Fireflies Glow?

Why do Fireflies Glow?

Matthew Lee Perlmutter

Fireflies have evolved the ability to send from their abdomen as a means of communication with each other. The most important reason for the flashing is for sexual communication. Flash signals have been classified into two systems. One is where a continuously glowing female attracts a non-glowing male. The second is when a female, flashes a species-specific response to a flying male, who is broadcasting a pulsating signal. There are other functions of flashing as well, such as using their luminescence for lighting up the ground during landing and walking. Fireflies also flash when captured or confined, which is thought to intimidate predators. Males can sometimes bend his light organ forward and put it in the face of the female he's mounted, flash it, blinding her since her eyes are sensitive and adapted to darkness. She will then be unable to see rival males clearly, hindering her from communicating with other potential mates. (Lloyd, 1984a).

A particular genus of firefly, Photuris, has evolved quite an interesting behavior. It has learned to mimic the mating flashes of another genus, Photinus. They have "cracked" the species-specific signal codes of their prey, using their own sexual signals against them (Lloyd, 1990). When Photinus males attempt to mate with Photuris, she eats them. This phenomenon is called either aggressive mimicry or predatory responding (Copeland, 1991). Twelve Photuris species have been observed preying on between two and eight other species of firefly. The species Photuris versicolor preys on the most, up to as many as eleven species. In fact, except for one species, Photuris congener, and a few other small exceptions, all know Photuris species prey on at least one other species of firefly. The other exceptions could have abandoned this behavior due to the lack of prey fireflies in a particular habitat, or the dangers of drawing larger species of Photuris to prey on them.

There is another beneficial, and quite interesting, reason for Photuris fireflies to consume Photinus fireflies, which has to do with defense from predators. Researchers at Cornell University in 1997 found that Photinus fireflies are protected from predators by chemicals called lucibufagins, which are steroidal toxins similar to the ones produced by Bufo toads. Spiders, bees, birds or any other predator will usually eject the firefly shortly after being eaten,