Insect of the Week: A Guide to Lightningbug Linguistics

Ever wish you could understand what the fireflies are saying? Well, you can!

The fireflies you’ll see most often in the eastern United States belong to one of the 34+ species of Photinus lightningbugs. These familiar fireflies fill our summer evenings with delight – they’re easy to catch because they fly at a leisurely pace, low above the ground. During summer months, different species make brief appearances, each with a mating season that lasts only a few weeks. Different Photinus species also start their courtship flashing at different times of night: certain species court just at dusk, while others wait until full darkness.

Taxonomically speaking, you need to inspect the male genitalia to really pin down Photinus species identifications. But many species also differ in the pattern and timing of their courtship flashes. So you can learn to distinguish species by paying close attention to the exchange of flash signals between males and females (using a stopwatch will help).

Photinus courtship goes like this: each evening, flying males advertise their availability by broadcasting a species-specific flash pattern. Females, who can fly but generally don’t, sit perched in vegetation and watch for males as they pass by. A females may respond to attractive male by curling her abdomen in his direction and giving him a flash back – it’s her “come hither” sign! When he flies closer and flashes again, they might strike up a conversation. This back-and-forth flash dialog will continue – often attracting other amorous males – until the pair finally meets and mates.

The guide below will help you decipher the distinctive courtship flash patterns given by 11 of our common Photinus species:

Here’s how to read the chart: for each species, the males’ flash patterns are shown in blue, next to the response flashes of their corresponding female (shown in red, note change in time scale).

The top six rows show species where the male flash pattern consists of a single pulse of light that’s repeated at fixed time intervals. You can recognize what Photinus species these males belong to by paying close attention to their flash timing. For instance, Photinus pyralis males give a leisurely flash (about ¾ of a second in duration), which they repeat every 5-6 seconds. In contrast, Photinus marginellus males emit a quick flash (less than ½  a second), and repeat this every 3 seconds.

The next three rows show Photinus species where males emit a double-pulsed flash pattern. Here it’s the time interval between the two pulses that differs among species; this interval ranges from about ½ second in Photinus consanguineus to 2 seconds in Photinus macdermotti. In the last two species males give multiple pulses that vary in the number and interval between pulses.

Female responses are illustrated on the right-hand side of the chart. Look down in the grass for females, and measure how long it takes them to answer a male’s flash. In Photinus marginellus, females will respond almost immediately (within less than a second), while Photinus ignitus females have a response delay of about 4 seconds.

With practice, you can use these flash patterns to recognize many different Photinus species, so step outside and have some fun! You can learn more about these courtship conversations in Silent Sparks: The Wondrous World of Fireflies.


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: How to Make Your Yard More Firefly-FriendlyInsect of the Week: Five Myths About Fireflies >>