Synchronous fireflies certainly highlight Earth’s natural magic, yet such cooperative behavior presents quite a thorny scientific paradox!
We do know how some fireflies manage to synchronize their flashing, thanks to work done in the 1960’s by John & Elisabeth Buck (previous post). For instance, male Pteroptyx fireflies in southeast Asia can reset their internal timekeeper whenever they see a neighbor’s flash. Inspired by Steve Strogatz’s book, Sync, Nick Case made a spectacular simulation to illustrate how this works – I’ve played with it for hours, and you can, too!
But why do fireflies synchronize? Why should thousands of males so carefully coordinate their behavior to flash in unison, all of them marching to the beat of a single drummer? According to sexual selection theory, these males should be competing fiercely with each other for the chance to mate. So why synchronize?
This paradox has gotten a lot of discussion, but we still don’t have a definitive answer. In Southeast Asia, thousands of male Pteroptyx fireflies gather together in particular display trees and flash synchronously to attract flying females. First studied by John & Elisabeth Buck (1968), this cooperative behavior could be one solution to the challenge of finding a mate while navigating the dense vegetation of tropical mangroves. The beacon hypothesis posits that if many males flash all together in a display tree (these are often located in a conspicuous spot along the water’s edge), they might enhance their visibility and thus increase their collective ability to attract some females. But once any female arrives at the display tree, we expect these same males to abruptly adopt some cutthroat tactics to win the female’s favor. For unless these synchronizing males can – on average – increase their own mating chances over that of a lone signaller, there can be no evolutionary advantage to male-male cooperation, however beautiful it may be.
Here’s a great news story about the U.S. synchronous firefly display in Elkmont, Tennesse. I especially love this quote – “It’s like the whole forest is breathing!”
Read more about the mechanisms and explanations for this astonishing firefly synchrony in Chapter 2 of Silent Sparks.