Fireflies are not really flies but are members of the beetle family and are beneficial. They are small (2cm), brownish black and have hard wings.
Firefliy (left), Firefly (right)- J.E. Llloyd, University of Florida
Their eyesight is not very good and they are not very intelligent so they rely on signals from females. Namely the light and flight pattern that she makes. There are other beetles that imitate the female and they will eat the males if they are tricked. There is a special organ on the underside of the abdomen that makes fireflies able to transmit light. The flashes of light fireflies emit can be white, green, yellow, orange or red. Some fireflies start flashing their light at dusk while others will do this only in full darkness. As a child I am sure that you must have been fascinated by these critters.
Larvae of firefly-photo unkown, Patten of firelies-photo W. Childress
Habit and Lifecycle
They are found in all tropical and temperate regions. There are about 2000 species but the populations have declined radically due to many man-made factors including pesticides, scientific research and possibly city lights. I have yet to see one here in my area of Texas where I live. Females lay their eggs in the soil and the eggs hatch within a month. Some species lay their eggs in trees. The larvae (glowworms) hatch and feed on other insects throughout the summer months for up to 2 years. When completed stages of larvae they dig tunnels in the soil and overwinter there. In the spring they emerge, feed and become adults after they pupate. Then the wonderful summer lightshows begin (for mating and also entertainment to those who love to see them).
Firefly larvae eat slugs and snails (also earthworms). It is unclear as to whether or not adults feed at all. Frogs will eat as many fireflies as they can.