Alex's Photinus lightning bug.
Most easterners have fond recollections of one of early summer's truly mysterious and magical biological events – the annual appearance of the first lightning bugs, a.k.a. fireflies. These are not true bugs like stink bugs or squash bugs. They are actually soft winged beetles. The production of the eerie greenish-yellow light is accomplished by a rather remarkable chemical reaction in cells lining the light organ of the beetle's abdomen. These cells called photocytes contain a chemical, luciferin. When combined with oxygen by an enzyme called luciferase, a reaction takes place that releases light. The immature stages or larvae, called glowworms, are found on the surface of the soil. They also produce light and are predators of soil-dwelling critters.
Lightning bug on the hunt for prey -- aphids beware.
The primary function of the adult's flashing light is to signal other members of the species. Usually the male lightning bug flies and flashes a characteristic signal to woo a potential mate waiting below in the grass. If the female likes his show, she flashes a response and connubial bliss ensues. While capturing fireflies in my lawn last night, I observed a weak and steady glow from a firefly below. When I actually found the flasher, I discovered a large female lightning bug devouring the front half of a hapless male, leaving only the rear end blinking in distress. What wicked behavior was this? It turns out that several species of fireflies in the genus Photuris can mimic the flash pattern of fireflies in the genus Photinus. When the female Photuris sees the ever-hopeful male Photinus flashing above, she lures him in by mimicking his mate's flash call, and once within reach this femme fatale eats him alive. Is this simply a control issue, some kind of gender statement? Not really, lightning bugs are predators. They feed on many kinds of soft-bodied prey in our landscapes, including pests, but in turn they are food for their own predators. Photinus lightning bugs produce a defensive compound called lucibufagin that repels predators such as spiders and birds. By eating the male Photinus, the female Photuris has a high quality meal and obtains a dose of chemicals she can use for her own defense - how clever!
References
For more information on lightning bugs visit the following web sites:
http://www.news.cornell.edu/science/Aug97/luredandliquidated.hrs.html
http://www.ent.msu.edu/Extension/WBY/bugging%20you%20articles/Lightening%20bug.htm