By Karl Anderson
for the Gloucester County Nature Club
Fireflies, lightning bugs, call them what you will, everybody knows what you are talking about. The first firefly of the season says unequivocally that summer is here. But these insects are beetles, not flies or bugs.
There are multiple species – something like 19 of them in New Jersey – not all of which are nocturnal and not all of which are luminescent. But only two are common – the eastern firefly (Photinus) which is about a half an inch long, and the Pennsylvania firefly (Photuris) which is a little larger but otherwise very similar in appearance. It is the State Insect of Pennsylvania.
The unique feature of the nocturnal fireflies is their light, which is used to signal the opposite sex that the insect is ready to mate. It is a cold light, produced by a chemical reaction in the terminal segments of the insect's body. Different species of fireflies have different flash patterns, which vary in the duration of each flash and the length of time between flashes.
The male Pennsylvania firefly has a characteristic and easily observed J-shaped flight trajectory, with the light produced on the upswing. Females of our common firefly species remain on the ground or perch on vegetation during courtship, but they give flash responses to encourage prospective mates. Firefly larvae also glow in the dark, but it's a faint and continuous glow.
Like all beetles, fireflies go through a four-stage life cycle: egg to larva to pupa to adult. After mating, the female lays her eggs on the ground, usually among moist leaf litter or on rotting wood. The eggs hatch in three to four weeks. The larvae are predators and feed on insects, earthworms, snails and slugs. They hibernate underground over the winter, come out in the spring, feed for a while, then pupate for a week or two, emerging as adults in June and July. Adults live only long enough to mate and lay eggs, and do not need to eat. Both they and the larvae appear to be distasteful to predators.
Fireflies are in decline world-wide, presumably due to habitat loss. It is a bit surprising that we still see any of these insects in our suburban environment of well- tended lawns and pesticide-sprayed plants. Light pollution also seems to be playing a part. Car headlights, street lights, and yard lights all make it difficult for fireflies to signal each other during mating. Populations now are fragmented and some areas have more fireflies than others. Some have none. But if you want to see a good display of firefly courtship, try to visit a damp meadow on a warm early summer night.
For information about the Gloucester County Nature Club, see gcnatureclub.org/
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