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Illustration by Danielle Lamberson Philipp

1. Fireflies, or lightning bugs, are a type of winged beetle known for producing light. There are more than 2,000 species found throughout the world, over 150 scattered across the United States, and around two dozen inhabiting the Great Lakes area, including Wisconsin. Many of Wisconsin’s fireflies are most noticeable in June, July, and August, and it’s hard to miss the light show after sundown.

2. Their glow is produced by bioluminescence, which stems from a biochemical reaction involving a compound known as luciferin and the enzyme luciferase. (“Lucifer” translates from Latin as “light bearer.”) The reaction is highly efficient, converting roughly 90 percent of the energy into visible light that is often referred to as “cold light.” In contrast, inefficient incandescent light bulbs produce “hot light” because most of their energy is lost as heat. The flash patterns and colors that each firefly species produces through bioluminescence can differ slightly, and some species only produce light in the larval stage, not as adults. Flash colors range from orange to yellow to green and even blue. In most cases, the flash pattern is used for communicating with potential mates, although some deceptive fireflies are known to mimic the flash pattern of another species to lure and then ambush potential prey.

3. Fireflies can be a boon for your yard — at least, their larvae can. The black and pink juvenile fireflies, sometimes called glowworms because they also produce bioluminescent light, have an armor-plated appearance and live in damp areas, where they feed on slugs, snails, worms, and other soft-bodied creatures. Anyone with hostas, marigolds, or other low-growing plants in their yard has likely noticed the feeding damage from slugs in these past few rainy years, but fireflies may help minimize the harm that slugs cause by thinning their ranks.

4. Fireflies can be distasteful or even poisonous to predators because they harbor defensive steroids called lucibufagins. These steroids are related to toxic chemicals that certain toads release when injured or threatened. Not all fireflies possess these chemicals, but some species in the Great Lakes region are among those that do, and they wield a potent defense and deterrent against predators such as spiders, bats, mice, and birds.

5. Scientists have raised concerns that fireflies may be in decline, and there could be a number of factors involved. Habitat loss and light pollution with changing land-use patterns may be important parts of the puzzle, and pesticides may play a role as well. Anyone interested in helping fireflies in their yard can do so by reducing light pollution, avoiding pesticides, and keeping some “wild” areas on the property as potential firefly habitat. To learn more about fireflies and get involved with a citizen science monitoring project, visit Firefly Watch.

P.J. Liesch, better known as UW–Madison’s “bug guy,” is director of the Insect Diagnostic Lab in the Department of Entomology and an entomologist with UW Cooperative Extension. Much of his job involves communicating insect information to the public and acting as a bug identification guru for curious residents and businesses from all over Wisconsin.