Fireflies
A firefly’s glow is a chemical reaction called bioluminescence, and each species flashes its own coded pattern to find a mate. These guides cover how the light works, why populations are declining, and where to see them.
Harmless and quietly helpful; the larvae eat slugs and snails. Turn the porch light off and enjoy them.
Size
5 to 25 mm
small soft-bodied beetles
Diet
Larvae hunt snails
many adults barely feed
Habitat
Damp meadows, banks
woodland edges, streamsides
Light
Cold bioluminescence
a coded flash per species
Family
Beetles, not flies
around 2,000 species
Life cycle
Even the young glow. A firefly spends most of its life as a predatory larva underfoot.
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Egg Laid in damp soil or moss; in some species the eggs themselves give off a faint glow.
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Larva A glowworm. It spends months, sometimes years, hunting snails and slugs in the leaf litter.
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Pupa It pupates in the soil or under bark, rebuilding into the flashing adult.
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Adult The familiar summer light. Many adults barely feed and live only to find a mate.
Fireflies were the reason I first stayed out past dark with a camera. They're in trouble now from light pollution and lost damp ground, and the single most helpful thing most people can do is switch off the outdoor lights on summer nights. Give them dark and they come back.
Sam Fielding · field note · about Sam
Typical season
A short window around midsummer; earlier in the south, later up north.
A firefly's glow is close to 100% efficient. Almost no energy is lost as heat, which is why it's called cold light.
