Fascinated by Fireflies

Sue Jagoda
September 16, 2008 | Life Science


Fireflies are just one of the signs that summer has arrived, at least here in Ohio. I've always been fascinated by these amazing insects with their flickering glow, but until recently when I heard a short story on a local news station, I hadn't thought about their relationship to some of the insects explored in various FOSS modules and courses. But once I heard that the glow worm was one stage in the firefly life cycle, my attention was caught. Here's some of what I've learned about fireflies (aka lightning bugs) since then.

Fireflies are soft-bodied, winged beetles. There are about 2,000 difference species of fireflies. Firefly adults are a little more than 1 cm long and live for about two months. There are more male fireflies than females by about fifty to one. After they mate, the female lays her eggs on or under the soil. About four weeks later the eggs hatch. The eggs and larvae of some species can glow. That's where the term "glow worm" originates. The larvae feed until the end of summer. The larvae survive the winter by burrowing underground or finding safe places on or under tree bark. They become active in the spring and begin feeding once more. After several weeks of eating, they pupate and emerge as adults. The larval diet varies from one species to another and includes other larvae, terrestrial snails and slugs, and possibly pollen and nectar.


Fireflies produce "cold light;" that's light containing no ultraviolet or infrared rays. The color of light can be pale red, yellow, or green. The light is due to bioluminescence, a chemical reaction that occurs in specialized light-emitting organs. Luciferin, a heat resistant substance located inside the firefly's abdomen, is the source of light. The trigger is Luciferase, an enzyme also located in the abdomen. ATP (adenosine triphosphate), a common compound found in plant and animal cells, provides the energy that causes the luciferin-luciferase mixture to light up.

In adults, bioluminescence is used primarily to locate mates. Many species have unique courtship flash patterns emitted by flying males in search of females. The females generally don't fly, but give off a flash response to attract males of their own species. It's interesting to note that some 90% of the energy a firefly uses to create light is actually converted into visible light. Compare that to an incandescent electric bulb that converts only 10% of its total energy into visible light and the rest into heat.

Some other tidbits of firefly information:

  • Fireflies were part of ancient Mayan mythology and were associated with the stars and Mayan gods.
  • The ancient Chinese sometimes captured fireflies in transparent containers and used them as lanterns. They thought fireflies came from burning grass.
  • Pennsylvania's state insect is the Pennsylvania Firefly (Photuris pennsylvanica), and the Common Eastern Firefly (Photinus pyralis) is one of the state insects of Tennessee.
  • The synchronized flashing of fireflies along the Selangor River in Kampong Kuantan, Malaysia, is a major tourist attraction and contributes considerable revenue to the local economy.
  • In European legend, a lightning bug flying in the window was a warning that someone was going to die.

You can easily see and maybe catch male fireflies about one hour before the Sun goes down. Stand in a grassy spot, and watch for small flickering lights hovering in the air. You can carefully cup your hands around a firefly, making sure you don't squeeze. You may be able to get the firefly to stick around until it sees a flash from a local female that it can't resist. When I was a kid growing up in Michigan, we used to pretend that we wearing firefly jewelry, like lapel pins.