Fireflies are not really flies but are members of the beetle family, Lampyridae, which consists of 1900 species across the globe including the glow worm. These nocturnal, luminous insects are becoming famous for their night time displays which have even been turned into tourist attractions.
    All known firefly larvae have photic organs and produce light. The most generally accepted hypothesis for why they can do this is that firefly larvae use their luminescence as a warning signal (aposematism) that communicates to potential predators that they taste bad due to defensive chemicals in their bodies. These larvae are also capable of increasing both the intensity and frequency of their glow
when disturbed. 
    Not all firefly species are bioluminescent as adults, but of the species that are, one or both sexes use a species specific flash pattern to attract a member of the opposite
sex. These bioluminescent signals can take the form of anything from a continuous
glow, to discrete single flashes, to "flash-trains" composed of multi-pulsed flashes 
    In most species of North American fireflies, during a certain time of night, males fly about flashing their species specific flash pattern. Females of the same species tend to be perched on vegetation, usually near the ground, and if a flashing male catches a female's fancy, she will respond at a fixed time delay after the last male's
flash.