The firefly - Photuris pennsylvanica (DeGeer) - was designated the official state insect of Pennsylvania in 1974. A small, unremarkable beetle by day, fireflies can transform a midsummer night into a fairyland of tiny, brilliant twinkling lights - a wonder of nature.

Commonly called "lightning bug" in Pennsylvania, the firefly produces light through an efficient chemical reaction using special photic organs, with very little heat given off as wasted energy. One or both sexes use species-specific flash patterns to attract members of the opposite sex (though not all firefly species are bioluminescent as adults).

These flashing signals range from a continuous glow, to discrete single flashes, to "flash-trains" (composed of multi-pulsed flashes). In most North American species of firefly (including Photuris pennsylvanica), the males fly about flashing their species-specific flash pattern, while females are typically perched on vegetation near the ground. When a flashing male attracts a female, she responds at a fixed time delay after the male's last flash. A short flash dialogue may ensue between the fireflies as the male firefly locates her position and descends to mate.

The firely is also a state symbol of Tennessee. Most states have adopted at least one insect symbol as a state insect, state butterfly, state bug, or state agricultural insect (see list of all state insects).

Source:

Pennsylvania - Symbols: PA Historical & Museum Comm.
State Symbols: Hello Pennsylvania
State Symbols: Pennsylvania House of Representatives
The Firefly Files: Ohio State U

Links:

Fireflies: Earth & Sky Kids Radio Shows
Illustrations of Larvae, Pupae, and Adults : U of Florida
Coleoptera: Lampyridae: Common Insects, U of Florida
State Insects - 50 States List