In the larval stage, which accounts for most of their life, Eat Lightning Beetle Snails, snails and earthworms.
As adults, many fireflies don’t eat at all – they’re only adults for a few weeks, so mostly they reproduce and die. females from the Photuris group are a notable exception. These “femme fatale” fireflies lure males from other groups with tantalizing flashes of lightning and then, as the nickname suggests, eat them. Keep that in mind the next time you’re in the backyard about them ooh and ahh.