Lewisburg, Pa. -- Late July is one of the best times in the Northern Hemisphere to watch the natural light show that fireflies put on.
According to Bucknell University professor Sarah Lower, a leading firefly researcher, that light show is at risk because artificial lighting disrupts the insects' life cycles; firefly populations are "blinking out" from the abundance of light pollution produced by humans.
“Light at night harms fireflies,” Lower says. “They use light to communicate, and their light is a mating signal. So if there’s a lot of ambient light around, they can’t see each other’s signals, and they can’t find each other to mate.”
The fireflies that we see each summer are adult beetles. Most adult fireflies only live for about two weeks - their only chance to find a mate and lay eggs. During the rest of the year, the eggs hatch into larvae and grow until pupating in summer.
Some fireflies have two-year life cycles, “so many of the fireflies we are seeing right now first hatched out of eggs in the summer of 2018,” Lower says.
Fireflies' blinking patterns is essential to the mating process. The beetles use light patterns to attract mates, sometimes blinking in unison to light a path to each other.
“An individual male has greater reproductive success in finding a female if they all signal together,” says Lower. “In Malaysia, where all of the males gather together and signal from a single tree, we think that is to identify a specific area where females know to go and mating can occur.”
This synchronicity gives fireflies a higher chance to mate and lay eggs.
To attract fireflies to your yard, Lower suggests that people: "Keep their lights off to minimize light pollution, make sure that there are spaces provided for their prey such as worms and slugs, and develop areas with vegetation to provide cover and moisture for the fireflies during the heat of the day."