By day, adult fireflies look like insignificant beetles. In fact, you and your kids probably wouldn't recognize one if you saw it resting on a nearby leaf. After all, fireflies don't bite, carry disease or cause significant plant damage. But when the sun goes down, they fascinate just about everyone, their twinkles lighting up the night.
Fireflies flash for several reasons: to attract a mate, to warn other fireflies of danger and to convince predators that they're not tasty morsels. (Apparently the chemicals that make the light do taste bitter.) Although other insects can produce light, fireflies are the only ones able to flash distinct signals. They store two rare chemicals in their abdomens: luciferin and luciferase, which, when mixed with oxygen, magnesium and adenosine triphosphate (ATP), produce light that gives off very little heat, a process called bioluminescence.
More than 170 species of fireflies (also known as lightning bugs) live in North America, and more than 1,900 species live in temperate and tropical areas across six continents. Each species exhibits particular habits. Some fireflies inhabit primarily open fields, some hunt for mates in wooded areas and others search over bogs and marches. Some flash at dusk and stop at dark, while others only light up when it's very dark. The genus Photinus flashes a yellow light, but Pyractomena gives off an amber glow and Photuris a green. In addition, each species sends different mating signals. The male Photinus pyralis beams a short flash as he rises making a J-shape. The female responds with a single flash. Photinus consumilis signals his potential mate with a rapid succession of flashes. She responds with two beams. Usually a male won't fly down to a female of the wrong species, but sometimes a femme fatale mimics the flickering pattern of another species; when the male moves in, the female eats him.
In Canada, the most common species is Photinus pyralis, approximately 10 to 14 millimetres long--the males are larger than the females. They are dark brown with orange and yellow accents and have dull yellow margins around their wing covers. At dusk, the warmest part of the night, Photinus pyralis males cruise a few feet above the ground flashing for an hour or so, waiting for a female, sitting on vegetation below, to signal to Mr. Right. The chosen male moves in slowly, his light dims, they meet…. A few days later, the female lays a hundred eggs or so just under the soil. After three or four more weeks, slightly luminescent larvae emerge to feed voraciously on soft-bodied insects, slugs and snails-fireflies make good garden friends. In fall, they burrow underground for winter. In late spring or early summer, after living one or two years in the soil, each larva builds a marble-sized mud protection around itself and changes into a pupa. And approximately ten days later, adult beetles emerge to eat pollen by daylight, twinkle by starlight and start the cycle over again.