Silent Sparks: The Wondrous World of Fireflies

By Sara Lewis

Princeton University Press, 2016; 240 pages, $29.95

One of the striking photos in this richly illustrated appreciation of lightning bugs is that of a male American big dipper firefly (Photinus pyralis) suspended in mid-flight with what appears to be a startled expression on his face. A blur of light traces the motion of his luminous rear end and his big bug eyes seem riveted on the camera, as if he’s been caught, in flagrante delicto, in a private dance for a prospective mate. Which he has, of course, for the glow and the motion are, to fireflies at least, all about sex.

Anyone who’s enjoyed their nocturnal sparkle over a summer lawn is familiar with that firefly mating dance, but Sara Lewis, a biologist at Tufts University, provides entertaining and informative program notes on why and how fireflies do it, and how it all fits into the evolutionary scheme of things. Surprises abound—fireflies live most of their life underground, we learn, spending as long as two to three years in the larval stage, fattening on earthworms, snails, and other insects. The feasts of youth, however, are all but forgotten when they finally emerge as adults, frantically looking for mates. During the two weeks that they live as adults they do not eat— males flit back and forth signaling their fitness in species-specific blinks, and females reply with flashes to indicate availability. As many as twenty males, responding to the seductive call, may pile on a hapless female in hopes of siring her brood. Eventually, a pair hooks up, copulating sometimes until dawn, after which the female crawls away to lay her eggs, while males, especially those unsuccessful in love, continue on until they run out of the energy reserves they accumulated as larvae.

Considering that fireflies are neither pests nor creatures of more than entertainment value to humans, there’s been a notable amount of study devoted to them. Scientists have programmed LEDs to mimic the male’s courting flashes, thus determining how to best seduce a female firefly. Blink as fast as you can, males: females seem to prefer patter singers to crooners.

Attractive as they are to humans, fireflies are surprisingly repugnant to other insect-eating creatures. Researchers have found that birds, lizards, bats, toads, and mice will avoid dining on fireflies once they’ve sampled a few. Fireflies not only smell and taste terrible (according to some adventurous entomologists) but are loaded with toxic steroids, a feature that’s helped them survive for ages despite their habit of advertising their presence so luminously on summer evenings. And though humans today threaten their survival with pesticides and habitat destruction, Lewis believes that we can do a lot to help by following her suggestions for making our own backyards more firefly-friendly. After all, she concludes, a world without fireflies is unthinkable, for “fireflies offer us the gift of wonder, an infallible recipe for falling in love again with nature.”