Fireflies, Lightning Bugs
Scientific Name: Family Lampyridae
Description: There are a number of different species of fireflies, none of which are actually flies—they’re beetles! They get the names “firefly” and “lightning bug” because of the flashes of light they naturally produce. This phenomenon is called bioluminescence, and the bioluminescent organs in fireflies are found on the underside of the abdomen. A similar group of organisms are glowworms. The term “glowworm” can refer to firefly larva or wingless adult females—some of which are not in the firefly family Lampyridae. Both glowworms and fireflies are bioluminescent. The important distinction is that fireflies have wings and glowworms do not.
Size: Up to 1 inch.
Diet: The larvae eat snails, worms, and slugs, which they inject with a numbing chemical to disable. Adults eat other fireflies, nectar, or pollen, although some don’t eat at all.
Typical Lifespan: Approximately 2 months in the wild.
Habitat: Found throughout the United States in parks, meadows, gardens, and woodland edges. They are easily seen on summer evenings.
Range: Fireflies are found in temperate and tropical regions on every continent except Antarctica.
Life History and Reproduction: All larvae are able to produce light to deter predators, but some species lose this ability in adulthood. Each species has its own pattern of light flashing, which is controlled by the nervous system. Some species, such as the Pennsylvania firefly (Photuris pensylvanica) are still bioluminescent as adults and use their flashes to attract mates of their species. This species also uses light to attract their prey, the big dipper firefly (Photinis pyralis), which they eat to obtain defensive chemicals. Aside from mating and prey attraction, it’s thought that bioluminescence may be a defense mechanism for the insects—the light lets predators know that their potential meal isn’t very tasty and might even be toxic!
Bioluminescence in fireflies is nearly 100 percent efficient, meaning that little energy is wasted to produce their light. By contrast, an incandescent light bulb is only 10 percent efficient—90 percent of the energy is lost as heat. For another comparison, the heat produced by a candle is 80,000 times greater than the amount of heat given off by a firefly’s light of the same brightness. Fireflies must be more efficient to save energy.
Conservation status: Anecdotal evidence suggests that firefly populations may be on the decline. Fireflies live in fields, meadows, forests, and other natural habitats. As these areas become fewer due to development, it’s important to welcome fireflies into your backyard!
- Evans, A. V. National Wildlife Federation Field Guide to Insects and Spiders of North America. Sterling Publishing Co., Inc.: New York, NY 2007.
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