The first week of summer marks the return of one of Mother Nature’s truly mysterious and magical biological events – the annual appearance of lightning bugs, a.k.a. fireflies. Lightening bugs are not “bugs” at all. Entomologists reserve this term for the “true” bugs like stink bugs, boxelder bugs, and bed bugs with sucking mouthparts and incomplete metamorphosis. Lightening bugs are actually soft winged beetles that have evolved a clever means of communication. 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 of lightening bugs are known as glowworms. They are found on the soil surface and in leaf litter and rotting wood where they eat other insects. As the name implies, glowworms also produce light. The primary function of the adult's flashing light is to signal other members of its species. Usually, at dusk 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 the happy couple mate. In addition to supplying sperm to fertilize the eggs of the lightning bug lady, the male also provides a packet of rich protein used by the female to provision eggs developing in her ovaries. This nuptial gift is important for the reproductive success of both the male and female lightning bug. While capturing fireflies in my lawn, I observed a weak and steady glow emanating from the grass below. When I located 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 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. Once in reach this femme fatale eats him alive. Is this simply a control issue, some kind of gender statement? Not really, lightening bugs are predators. They feed on many other kinds of soft-bodied prey including pests, but in turn, they are food for their own predators. Photinus lightning bugs produce defensive compound called lucibufagins that repel 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.
The fascinating studies of Dr. Sara Lewis and Dr. Thomas Eisner and his colleagues served as resources for this Bug of the Week. To learn more about lightning bugs, please visit the following web sites.