The flashes of fireflies are the lost ephemera of our youth. Most of us have fond memories of long, dusky summer evenings spent chasing and capturing lightning bugs in backyards or abandoned fields. We’d put them in an empty mayonnaise jar with holes punched in the lid and set them beside the bed, falling asleep to the cold, ghostly green flashes emanating from their abdomens. Sometimes we’d ask our parents why they glowed as they do; unless our mom or dad was an entomologist or amateur naturalist, they were usually as in the dark as we were. Well, there’s a simple answer, one our folks probably would have hedged anyway:
Sex.

North America has about 125 species of fireflies, or lightning bugs, as they are most commonly known. They aren’t flies at all, but small, soft-bodied black or brownish beetles classified in the family Lampyridae. The most common species in the United States is called Photinus pyralis. Fireflies emerge in spring as over-wintering larvae, which feed on other small insects and animals such as snails. Sometimes these larvae are luminous and are known as glowworms. The larvae pupate in early summer and after about two weeks emerge as the flying adults with which we are all familiar.

Not all species have the ability to produce light, but the nocturnal ones have an organ called a lantern in their lower abdomens that contains special bioluminescent cells. These cells contain the chemicals luciferin and luciferase, an enzyme. When exposed to oxygen, the chemicals react with a cold, heatless, glow. Some fireflies flash reddish-orange, some a greenish-yellow. It’s not an involuntary act, however, as the fireflies’ nervous systems control the flashing and its pattern.

Each species has its own flash language, and it’s the males who do most of the talking. They’re the ones you can see flying in the evening, while the females flash discretely from the undersides of leaves. When a female sees a male whose pattern she likes, she responds with the correct signal, and they mate. Well, most of the time. Some females mimic patterns, which lure unsuspecting males to their leaf lairs where they are overpowered and devoured. No one ever said dating was easy.

Some species of firefly found in Southeast Asia time their flashes to occur in unison, a phenomenon known as synchrony. It had never been confirmed in the U.S. until 1992, when a Tennessee woman noticed synchronous flashing in the Elkmont area of Great Smoky Mountains National Park. The species involved is called Photinus carolinus, though only those found at around 2,000 feet exhibit synchrony. Scientists are still unsure why the light show-which resembles a giant light being switched on and off-happens only near Elkmont. The three-week dusk display takes place in June and attracts human tourists as well as female fireflies.

Fireflies are still relatively common, though you won’t see many in urban areas where wetlands, meadows, and woods are scarce, and city lights replace the dark of night. Fireflies are numerous enough that they are collected for their luciferase, which, when extracted and crystallized, is useful in the laboratory for genetic research and in industry as a way to detect impurities in soft drinks. According to Analytical Luminescence Labs in Baltimore, Md., East Tennessee lightning bugs have the most potent enzymes. With luciferase going for 35 cents a gram, that means a lot of kids roaming neighborhoods at dusk, trying to capture lightning in a jar-for science and future memories.

William Cocke is always turning over rocks and rotten logs to see what’s underneath. He can be reached at wtc4q@virginia.edu.