Fireflies are best known for their showy nighttime displays, but not all fireflies flash at night. The common name “firefly” not only includes familiar flashing species (a.k.a. lightning bugs), but also the more cryptic glow-worms and daytime dark fireflies, whose adults—as their name suggests—are active during the day and rely on chemical pheromones rather than bioluminescence to communicate. Glow-worms, like flashing fireflies, are active during dusk or nighttime and use bioluminescence (but glowing, not flashing) to communicate. While males look like typical fireflies, glow-worm females resemble larvae; they cannot fly because their wings are short or absent. Fireflies face numerous challenges, including increasing light pollution, habitat loss, pesticide use, and climate change. These threats affect firefly species in different ways, depending on each species’ life history traits and specific habitat requirements.
Fireflies are not flies but actually beetles in the family Lampyridae. Like all beetles, they undergo complete metamorphosis with four distinct stages: egg, larva, pupa, and adult. The complete life cycle can take anywhere from a couple of months to two to three years, with the majority of the life cycle spent in the larval stage. Firefly larvae are voracious predators of soft-bodied invertebrates. They typically hunt for their prey in moist soil or marshy areas, using their mandibles to inject prey with paralyzing neurotoxins. Once their quarry is immobilized, they secrete digestive enzymes that liquefy the prey before consumption.
Most fireflies pupate underground or in rotting logs, although some attach to tree trunks. The adults typically emerge in late spring or early summer. Mild winters can lead to early emergence and larger numbers of fireflies, since these conditions may lead to better survival of overwintering larvae. Wet springs can also lead to earlier or larger displays, and these conditions may favor fireflies’ favorite prey.
The larvae of all firefly species are bioluminescent. However, not all adults are capable of producing light. In fact, fireflies can be split into three main groups depending on their style of courtship: daytime dark fireflies, which are active during the day and do not produce light; glow-worm fireflies, whose flightless females produce long-lasting glows; and flashing fireflies (a.k.a. lightning bugs), which are probably our best-known fireflies due to the quick, bright flashes they produce.
Fireflies are found all over the world in temperate and tropical areas, on every continent except Antarctica. More than two thousand species have been described, with approximately 170 species documented in the United States and Canada. More species are being discovered and described each year.
We recommend these great guides:
- Fireflies, Glow-worms, and Lightning Bugs by Lynn Faust
- Silent Sparks by Sara Lewis
- Field Guide to Western North American Fireflies by Larry Buschman