Insect of the Week: the Darkest Fireflies

Bioluminescence lights up the larval stage in every member of this beetle family (Lampyridae), but adult fireflies have evolved remarkably diverse ways to find mates. Summertime icons that fill the night with their flashy courtship displays, the lightning bug fireflies might be the most spectacular. Yet many fireflies lose their bioluminescent spark once they become adults. These dark fireflies are active during the daytime, and females emit chemical signals to attract males. Phylogenetic evidence suggests that the common ancestor of all fireflies also had nonluminous adults. Though they are often overlooked, today these dark fireflies can be found coast-to-coast across the United States and Canada. Two groups of dark fireflies are particularly common. Once you learn to recognize them, you will see them everywhere!

A Lucidota atra firefly. Photo credit: Molly Jacobsen

Ellychnia includes a dozen or so different species with nonluminous adults. These dark fireflies are close cousins to the Photinus lightning bugs, but they have evolved a radically different lifestyle. Sometimes called Winter Fireflies, the adults spend the winter wedged down into grooves on tree trunks. They prefer trees with deeply furrowed bark, and dozens are often seen congregating on a single tree. After hunkering down for several months, surviving snow and freezing temperatures, Ellychnia adults are among the first insects to become active in the spring. Mating takes place in late March and April, when these hardy beetles can be seen flying slowly through wooded areas. Mating pairs, attached tail-to-tail, are commonly seen on tree trunks, where they remain coupled for 12 hours or more. It has been proposed that Ellychnia, which evolved from a nocturnal, Photinus-like ancestor, shifted to become day-active to escape night-time hunters like the predatory Photuris fireflies.

Lucidota atra is another day-flying, non-luminous firefly, and these adults are simply stunning. They are also easy to identify with their jet black wing covers, brightly colored head shield and flattened, saw-toothed antennae. These dark fireflies are commonly seen in early summer as they fly slowly, just a few feet above the ground, across lawns, fields, and forests. Experiments done by Jim Lloyd in the 1970s revealed that Lucidota females release pheromones that are carried on the wind, creating an invisible plume. Males seek out females by flying slowly back and forth until they encounter a plume, then fly upwind until they reach the female. The chemical nature of the female pheromone remains unknown.


Sara Lewis, who has been captivated by fireflies for nearly three decades, is a professor in the Department of Biology at Tufts University. Her work has been featured in numerous publications, including the New York Times, Scientific American, and USA Today. Lewis lives with her husband in Watertown, Massachusetts.

silent sparksSilent Sparks
The Wondrous World of Fireflies

For centuries, the beauty of fireflies has evoked wonder and delight. Yet for most of us, fireflies remain shrouded in mystery: How do fireflies make their light? What are they saying with their flashing? And what do fireflies look for in a mate? In Silent Sparks, noted biologist and firefly expert Sara Lewis dives into the fascinating world of fireflies and reveals the most up-to-date discoveries about these beloved insects. From the meadows of New England and the hills of the Great Smoky Mountains, to the rivers of Japan and mangrove forests of Malaysia, this beautifully illustrated and accessible book uncovers the remarkable, dramatic stories of birth, courtship, romance, sex, deceit, poison, and death among fireflies.

The nearly two thousand species of fireflies worldwide have evolved in different ways—and while most mate through the aerial language of blinking lights, not all do. Lewis introduces us to fireflies that don’t light up at all, relying on wind-borne perfumes to find mates, and we encounter glow-worm fireflies, whose plump, wingless females never fly. We go behind the scenes to meet inquisitive scientists who have dedicated their lives to understanding fireflies, and we learn about various modern threats including light pollution and habitat destruction. In the last section of the book, Lewis provides a field guide for North American fireflies, enabling us to identify them in our own backyards and neighborhoods. This concise, handy guide includes distinguishing features, habits, and range maps for the most commonly encountered fireflies, as well as a gear list.

A passionate exploration of one of the world’s most charismatic and admired insects, Silent Sparks will inspire us to reconnect with the natural world.

This post is part of a series, explore additional posts here<< Insect of the Week: the American LadyInsect of the Week: How to Make Your Yard More Firefly-Friendly >>