A close-up photo shows a firefly sitting on a leaf.
Photo by Paul Seevers.

It’s a dark and steamy night. … No, this isn’t the beginning of a horror story, but one of a love story! A favorite thing of mine to do is to sit out on the front steps on summer evenings in June and early July and watch the lightning bugs flash. It seems to come and go in waves. One will start and be followed by many flashes. Then the sky goes dark for a bit and then it begins again. The love story part fits right here. This is their season, and the timing varies a little each year depending on temperatures and humidity levels.

Lightning bug flashes are a form of communication between males and females. Often, the females are hidden on the ground, in the grass or under leaf litter. The males fly around, flashing their lights in a pattern unique to their own species, and those are the ones we are most likely to see. The female’s response flash is often very different from the male’s. Hers is a softer light, shorter in duration and often directly pointed toward the male, making it go unnoticed by most people. There is one species however (Photuris spp.), where the females will mimic another species’ flash pattern (Photinus spp.), coaxing the males of that species to land looking to mate. But instead, she makes a meal out of him!

A female Photuris spp. lightning bug eating a male Photinus spp. lightning bug.
This female Photuris spp. firefly tricked a male Photinus spp. firefly into being her dinner. (Photo by Paul Seevers)

While it is believed that most adult lightning bugs do not eat, that they are just interested in mating and laying as many fertilized eggs as possible, there is evidence of the adults eating nectar from flowers. For most lightning bug species, adults only live one to four weeks. The egg stage is also brief, lasting two to three weeks. Depending on the species, the eggs will be laid singly or in clutches of a few to more than 100 eggs! The eggs are barely visible to the human eye. Firefly eggs need moisture, so the higher humidity of summer and the climate of where the eggs are laid is crucial. Often the eggs are laid in leaf litter or rock crevices. The larval stages will last one to two years and during this time, they are predacious – you could even say they are eating machines!

If conditions are favorable, the time spent in this larval form is shorter, about one year. If conditions are not favorable, it will take longer for them to develop. Food resources, rainfall and temperature all play a major role in how long it takes for them to develop. The larval forms eat earthworms and soft-bodied insects like caterpillars, snails and slugs.

A close-up photo shows the underside of a firefly.
A New Perspective: The underside of Photinus spp. (Photo by Paul Seevers)

As larvae, fireflies will go through four to seven instars (a developmental stage between each molt) or molts. The tougher outer covering of the larvae does not grow, so in order for them to actually grow, they have to shed that. When the time is right for the last molt, they will find the appropriate spot to pupate. During this phase, the larval form will metamorphosis into the adult form. It can take anywhere from seven to 21 days, depending on the species and environmental conditions. When the adult emerges, it will take time to darken, harden its exoskeleton and prepare its wings for flight. This can take several hours.

There are more than 2,000 species of fireflies worldwide, found on every continent except for Antarctica. Over 125 of those species call North America home, and they are spread throughout the United States, although the eastern portion of the U.S. has more than the west. It seems more of the non-flashing fireflies are found out west, but we do have some non-flashing varieties in Ohio too. They are diurnal (meaning they are active during the daytime) and have no lanterns that flash or glow. It seems that in all, fireflies or lightning bugs of all phases glow, except in the species where the adults have lost their lantern. For some species, the glow of the eggs is so faint, that it cannot be picked up by the human eye!

Fireflies, Glow Worms, and Lightning Bugs: Identification and Natural History of the Fireflies of the Eastern and Central United States and Canada

There are so many fascinating things about lightning bugs/fireflies and I cannot possibly share all that I am learning in this blog. However, if you want to learn more, I suggest reading “Fireflies, Glow-worms, and Lightning Bugs” by Lynn Frierson Faust. It is a very engaging book, full of scientific information written in such a way that keeps your attention and doesn’t overwhelm you. It has also been highly recommended to me to read “Silent Sparks: The Wondrous World of Fireflies” by Sara Lewis.

In the meantime, grab a cold drink and head out to a comfy spot this evening and try to catch the last of the lightning bugs’/fireflies’ annual show. I guarantee it’ll be one of the best activities you will do all summer!

Amy Roell
Director of Programming