Scattered reports of the first fireflies flashing in a few backyards in Pennsylvania began to surface last weekend.
That was ahead of schedule for most lightning bugs, which will be emerging from the soil over the next few weeks, building to the peak of flight in mid-June through July and then trailing off through August, according to Firefly Watch, a national monitoring effort focused on the insects managed by Massachusetts Audubon.
The heavy rains that have spread across Pennsylvania in recent weeks could signal good things for fireflies this summer, as the best flights of the insect occur in summers that follow springs with above average rainfall.
Regardless of weather patterns, the flashing insects won’t be seen over as many backyards or in as many parks as they were a few decades ago.
Widespread use of pesticides and herbicides has been reducing the insect’s range and numbers over the past several decades. If you don’t see any fireflies in your backyard, that could be an indicator that the application of chemicals on the site has created a dead zone for lightning bugs and many other species.
Increasing areas of paved surfaces also lead to reduced firefly populations.
The firefly spends most of its life in the soil, from egg through predatory, wormlike larvae through the cocooned pupa. Only the adult stage lives much aboveground and in the air, and then only for a few weeks.
Weather also will play a significant role in how active the adult fireflies will be after they emerge. Warmer, more humid nights will see much more activity, as well as more frequent flashes.
When evening temperatures dip below 60 degrees, firefly activity drops off noticeably. Like other insects, fireflies are cold-blooded. They rely on heat from their environment to perform much of their activity.
Dozens of things you probably never knew about fireflies
Fireflies produce their glow through an internal chemical reaction known as bioluminescence. They carry the chemical luciferin in their abdomens. When luciferin mixes with oxygen and the enzyme luciferase, a chemical reaction occurs that lights up their abdomen.
A firefly’s light is cold and does not lose much energy as heat. That’s important, because if a firefly’s glowing abdomen heated, like a burning lightbulb, the insect would not live through its own flashing.
There are more than 2,000 species of fireflies worldwide, a couple dozen in Pennsylvania including the Pennsylvania firefly (Photuris pennsylvanica), which was designated the official state insect of Pennsylvania in 1974.
