The Firefly Life Cycle

The 4 Stages of the Firefly Life Cycle

Firefly larva.
Firefly larvae look quite different from the familiar adults. Getty Images/Hans Lang

Fireflies, also known as lightning bugs, are part of the beetle family (Lampyridae), in the order Coleoptera. There are about 2,000 species of fireflies worldwide, with over 150 species in the U.S. and Canada. 

Like all beetles, fireflies undergo complete metamorphosis with four stages in their life cycle: egg, larva, pupa, and adult.

Egg (Embryonic Stage)

The firefly life cycle begins with an egg. In mid-summer, mated females will deposit about 100 spherical eggs, singly or in clusters, in the soil or near the soil surface.

Fireflies prefer moist soils, and will often choose to place their eggs under mulch or leaf litter, where the soil is less likely to dry out. Some fireflies will deposit eggs on vegetation rather than directly in the soil. Firefly eggs usually hatch in 3-4 weeks.

The eggs of some lightning bugs are bioluminescent, and you may see them glowing dimly if you're lucky enough to find them in the soil.

Larva (Larval Stage)

As with many beetles, lightning bug larvae look somewhat worm-like. The dorsal segments are flattened and extend to the back and sides, like overlapping plates. Firefly larvae produce light, and are sometimes called glowworms.

Firefly larvae usually live in the soil. At night, they hunt slugs, snails, worms, and other insects. When it captures prey, the larva will inject its unfortunate victim with digestive enzymes to immobilize it and liquefy its remains.

Larvae emerge from their eggs in late summer, and live through the winter before pupating in the spring.

In some species, the larval stage lasts well over a year, with the larvae living through two winters before pupating. As it grows, the larva will repeatedly molt to shed its exoskeleton, replacing it with a larger cuticle each time. Just before pupating, the firefly larva measures about ¾" in length.

Pupa (Pupal Stage)

When the larva is ready to pupate, usually in late spring, it constructs a mud chamber in the soil and settles inside it. In some species, the larva attaches itself to a tree's bark, hanging upside down by the hind end, and pupates while suspended (similar to a caterpillar).

Regardless of which position the larva assumes for pupation, a remarkable transformation takes place during the pupal stage. In a process called histolysis, the larva's body is broken down, and special groups of transformative cells are activated. These cell groups, called histoblasts, trigger biochemical processes that transform the insect from a larva into its adult form. When the metamorphosis is complete, the adult firefly is ready to emerge, usually about 10 days to several weeks after pupation.

Adult (Imaginal Stage)

When the adult firefly finally emerges, it has only one real purpose, to reproduce. Fireflies flash to find a mate, using a species-specific pattern to locate compatible individuals of the opposite sex. Typically, the male flies low to the ground, flashing a signal with the light organ on his abdomen, and a female resting on vegetation returns his communiqué. By repeating this exchange, the male homes in on her, and the rest of the story is happily ever after.

Not all fireflies feed as adults—some simply mate, produce offspring, and die. But when adults do feed, they are usually predacious, and hunt other insects. Female fireflies sometimes use a bit of trickery to lure males of other species closer and then eat them. Not much is known about firefly eating habits, however, and it is thought that some fireflies may feed on pollen or nectar.

In some species, the female adult firefly is flightless. She may resemble a firefly larva, but have large, compound eyes. And some fireflies don't produce light at all. For example, in the U.S., species found west of Kansas don't glow.

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Hadley, Debbie. "The Firefly Life Cycle." ThoughtCo, Mar. 2, 2018, thoughtco.com/life-cycle-fireflies-lightning-bugs-1968137. Hadley, Debbie. (2018, March 2). The Firefly Life Cycle. Retrieved from https://www.thoughtco.com/life-cycle-fireflies-lightning-bugs-1968137 Hadley, Debbie. "The Firefly Life Cycle." ThoughtCo. https://www.thoughtco.com/life-cycle-fireflies-lightning-bugs-1968137 (accessed May 27, 2018).