The National Wildlife Federation

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Fireflies

Fireflies

Family: Lampyridae

Status: Not Listed

Classification: Invertebrate

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. Fireflies can reach up to one inch (2.5 centimeters) in length.

Range

Fireflies are found in temperate and tropical regions on every continent except Antarctica. They live throughout the United States in parks, meadows, gardens, and woodland edges. They are most commonly seen on summer evenings.

Diet

Firefly 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.

Life History

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. A firefly typically lives for approximately two months in the wild.

Conservation

Anecdotal evidence suggests that firefly populations may be on the decline. Fireflies live in fields, meadows, forests, and other natural habitats, and these areas are becoming fewer due to development.

Fun Fact

Bioluminescence in fireflies is nearly 100 percent efficient, meaning 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.

Sources

Disappearing Fireflies, Firefly.org

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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