Some firefly species perform synchronized flashing, i.e. flashing of a large number of fireflies at the same time. Areas where this phenomenon occurs include Southeast Asia (particularly near Kuala Selangor in Malaysia) and the Great Smokey Mountain National Park (near Elkmont, TN). Current hypotheses about the causes of this behavior involve diet, social interaction, and altitude. A small population in the Congaree National Park also performs synchronized flashing.
During copulation Photinus males transfer a spiral, gelatinous spermatophore to the female: sperm are released into the female’s spermatheca for storage, while the remainder of the spermatophore disintegrates within a specialized gland. Radiolabelling studies indicate that male-derived protein is used to help provision the female’s developing oocytes, and multiply-mated females show increased fecundity. As most Photinus adults do not feed, these studies suggest that females should continue to forage for matings to supplement their diminishing larval reserves, even after they have gained sufficient sperm to fertilize their eggs.
Female Photuris fireflies are known for mimicking the mating flashes of other "lightning bugs" for the sole purpose of predation. Target males are attracted to what appears to be a suitable mate, and are then eaten. For this reason the Photuris species are sometimes referred to as "femme fatale fireflies."
Most fireflies are quite distasteful and sometimes poisonous to vertebrate predators. This is due at least in part to a group of steroid pyrones known as lucibufagins (LBGs), which are similar to cardiotonic bufadienolides found in some poisonous toads.