People often ask me this excellent question. Yet it doesn’t have a quick or easy answer. One reason is that different species live in different habitats. For instance, the salt marsh firefly Micronaspis floridana is restricted to intertidal regions along the Florida coast. Another reason is that certain things matter to adult fireflies, whereas different things matter to the juveniles.
For adult fireflies, what’s most important is finding a dark place for their courtship displays. Artificial lights – streetlamps, outdoor security lights, even car headlights – can disrupt firefly courtship conversations. Such bright backgrounds make it difficult for fireflies to see each other’s courtship signals. Another desirable habitat feature for adult females is easy access to suitable egg-laying sites, like moss, moist soil, or decaying wood.
Fireflies need moisture during all of their life stages. Recall that in the U.S., larval fireflies spend 1-2 years living underground. There, they feast on earthworms, slugs, and snails. These terrestrial firefly larvae require consistently moist, undisturbed soils with abundant prey.
So how can you improve your local firefly habitat?
Most importantly, give those courting adult fireflies a bit of privacy! Simply turn off your outdoor lights during firefly season. Contact the Public Works department in your town or city to see if they’re willing to turn off or dim any unnecessary security lights around public buildings during firefly season. In Japan, many communities install temporary shields on their streetlamps to keep light from spilling out into firefly habitat.
To improve habitat for larval fireflies, let your grass grow a bit longer between mowings – taller grass retains more moisture. Let some leaf litter, moss, or woody debris accumulate around the edges of your property. Finally, don’t apply broad spectrum insecticides to your lawn; chemicals that are designed to eradicate other beetles will also kill fireflies.