U.S. Fireflies Flashing in Unison

Science News,  March 13, 1999  by Susan Milius

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Case, the only scientist so far to describe a synchronous Asian species actually mating, reports that males keep on flashing as a female lands in their midst. The male who triumphs in attracting her favors swivels his abdomen around so that his lantern blasts on and off right in front of his partner's eyes during the entire coupling. "It's to keep her mind off the other males," Case speculates.

Clearly, the flashing has something to do with mating. Males may be sending a neon message as direct as "Over here, girls!" But why broadcast it at nearly the same millisecond as thousands of other equally available guys?

"It's not mystical," grumbles James Lloyd of the University of Florida in Gainesville. He protests against a tendency to elevate synchrony to the status of unexplainable phenomenon.

In Buck's 1988 review of the field--a 50-year update of his first scientific review of the literature--he mentions nine hypotheses to explain synchrony. One suggests that flashing in unison aids the females in picking out the rhythm of the right species. Another proposes that females essentially get temporarily numbed by a flash and can't perceive or respond to a subsequent flash unless they get a brief resting period, so there's no point in one individual's lighting up before the others. Another idea was that a male would flash in unison with a neighbor already flirting with a female. That way he might get a chance to steal her fancy.

Copeland says that he wouldn't be surprised if the synchrony in Elkmont guarantees a nice, dark moment for roving males to get their bearings on the faint answering wink of a female, without the interference of some other hotshots showing off their flashers. "The male is enormously bright--it's just dazzling," he reports. He and Andrew Moiseff of the University of Connecticut in Storrs are just starting to work on the synchronicity of the coastal flashers.

Detecting males synchronizing for any reason can be tricky, he cautions. Insects can fall into phase just by chance, flashing together for cycle after cycle. Even traffic cones with flashing caution lights can seem to fall in step for six to eight cycles and then drift out of synch again. Copeland has demonstrated this illusion of synchronicity by visiting a road repair site at 3 a.m. and filming the traffic cones for a while.

"If you have to stretch and strain to see it, it's not there," he advises synchronicity hunters. Just by chance, fireflies often blink together for five, six, or more cycles before falling out of phase. However, fireflies that stay in synch for 3 or 4 minutes, and hundreds of flashes, merit serious attention.

He remembers his own experience seeing the Tennessee flashers for the first time. Thrilled with the discovery, he phoned Moiseff to tell him the males were synchronizing. "I said, `Andy, it's absolutely obvious,' and he said, `Prove it.'"

Copeland then spent the summer videotaping fireflies, recording flash activity of individuals in cages, and working through the data a few milliseconds at a time. With just a touch of crankiness, Copeland recalls that the next year, "when Andy finally came down and saw it, after about 30 seconds, he said, `It's obvious.'"

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