Q How do fireflies glow?
— Ryan Hopp, Verona, Wis.
A PJ Liesch, director of the University of Wisconsin-Madison Insect Diagnostic Lab:
Fireflies, sometimes called lightning bugs, are actually a type of beetle, so they’re not a true fly.
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In Wisconsin and the Great Lakes area there are about two dozen or more different species of firefly, and they all have slightly different habits in terms of when and where they flash and if they can flash. Their life cycle typically lasts a year or two, and they tend to live in damp areas.
Fireflies have a particular chemical called luciferin that interacts with an enzyme called luciferase. In the presence of certain other compounds and chemical elements like magnesium ions, it produces a glowing light. When living creatures produce and emit light it’s called bioluminescence.
The main reason fireflies glow is to find a mate, but they can also light up under other situations as a warning to others. Usually male fireflies fly around and flash light to advertise to the females. If a female is interested, she will send out a brief flash as a reply to the males.
Fireflies produce light very efficiently. An incandescent light bulb is really inefficient and a case where some energy is spent producing light but a lot of energy is lost as heat. Fireflies, on the other hand, stay very cool and would not be picked up on infrared cameras. In bioluminescence, almost all of the energy goes into that chemical reaction to produce light with very little lost as heat.
The process of catching fireflies can be a neat experience for children, but a catch-and-release method is advised. You can catch them in a jar and observe them for a couple of hours or a day at most and then should release them in the same area they were found so they can return to their environment.