Five Fascinating Facts about Fireflies

While bugs can take the fun out of summer, there’s one insect that everyone loves: the firefly.

The firefly or lightning bug restores the kid in all of us. You just want to get up close to one; maybe capture it for a moment in your cupped hands and peek inside to see the flashing green glow. Then you let it go. You know it won’t sting. It won’t bite. And its light doesn’t burn.

But what is this fascinating little creature?

1)     The firefly is actually not a fly. And it’s not a bug. It’s a beetle. These soft-bodied beetles usually have a head hidden under a shield, called a thoracic shield. They’re in the family of Lampyridae, or “glow worm.” There are about 20 species of fireflies in New Hampshire.

2)      That term, glow worm, really applies to the larvae, which live underground in the winter. While all known firefly larvae glow to one extent or another, not all of the adults glow. For larvae, glowing seems to be a message to would-be predators: “Don’t eat me! I’m toxic!” Chemicals in the larvae are indeed poisonous or distasteful to insects and other predators. Larvae themselves are predators of earthworms and larvae of other insects.

3)      In adults, fireflies’ capacity for “bioluminescence” is a different story. When you see fireflies this time of year, it’s usually in an open area, like a field, marsh, or lawn. And it’s usually a male, like the species Photinus pyralis, making its glowing J-shaped flight pattern. His flashing bursts are messages to the female: “I’m here! Look at me. Where are you?” The female, meanwhile, is usually hunkered down on the ground, with a much more subtle glow: “Psst! I’m over here, silly! Come on over.” 

4)      Some firefly species really put on a show for the ladies. In big groups, they synchronize their flashes, like amorous fireworks displays. On river banks of Malaysian jungles, one species synchronizes its flashes with choreographed precision, by the thousands. Must be quite a sight. Another species performs this synchronized glowing dance in the Great Smoky Mountains in early June. 

5)      Their glow comes from a chemical reaction produced in special organs in the lower abdomen. The process involves magnesium, oxygen and the light-emitting compound luciferin. It’s a cold light, producing no heat at all. A form of luciferin produced in the lab is used in medicine and genetics research for detecting magnesium and other properties. Even the U.S. military is interested in the bioluminescence of fireflies. Among the possible uses are creating landing zones for helicopters and identification markers to distinguish friendly soldiers and weapons from enemy.

You can learn more about the fireflies in your neighborhood by observing them. Follow an individual firefly and keep track of its Morse-code-like flashing pattern. You can also use a flashlight to trick fireflies. Put the flashlight low to the ground and turn it on and off quickly, just a little. Watch the male fireflies approach!

If you capture fireflies and put them in a jar, be sure to poke some holes in the lid so they can breathe. You can find several different species over the course of the summer. Be sure to let them go!