Minnesota Profile

Fireflies (family Lampyridae)

Vital Statistics

These light-producing beetles, also known as lightning bugs, occur throughout Minnesota. Firefly scientific names refer to their light-producing capability, such as Pyractomena from Greek root pyr meaning "fire." Seven genera and 15 species have been recorded in Minnesota based on museum records. Our largest species, P. borealis, found in Itasca State Park, is nearly 3/4 inch long. The range and abundance of Minnesota’s species are not known. Fireflies are most common east of the Rockies.

Appearance

While most beetles have hardened elytra (modified forewings that protect the flight wings), fireflies have soft elytra. Either thin antennae or long, saw-toothed antennae grow above or between bulging compound eyes. Larvae and adults have biting mouthparts. The light-producing organs, when present in the adults, are visible at the rear of the abdomen.

Habitat

Minnesota fireflies show up in forest clearings, large meadows, and prairies in the countryside and suburbs. Larvae live in moist habitats such as leaf litter, wetlands, and stream edges.

Life History and Biology

Adults emerge in early summer and search for mates at dusk. Males and females find each other by exchanging light flashes or emitting chemicals called pheromones. In flashing species, males cruise and flash at or above tree line at the edge of meadows. Females usually sit on bushes and other low plants, and wait for the right male before flashing a return signal. Each species has a typical number, length, and pattern of light flashes—a Morse code of light. Males of different species may further distinguish their signals by flying straight during the long flashes or by diving. An interested female responds with her own sequence of light pulses. After mating, the female lays eggs singly or in groups on the ground or in the soil between grass roots. After 13 to 27 days, eggs hatch and larvae live at or below soil surfaces.

What Lights Them Up?

Fireflies produce cold light in modified fat body tissue. The pH of the firefly’s fat body tissue regulates light color, producing species-specific hues of yellow to orange. Firefly eggs, larvae, and wingless larvalike females of some species produce steady light, and are sometimes called glowworms.

Food

Larvae voraciously feed on other insects, earthworms, slugs, and snails. They track slime trails to prey and stun them with poison injected by their mandibles. Adult diet is not well-documented.

Susan Weller, University of Minnesota entomologist