The sky can bring many wondrous signs of summer's arrival. One of the most welcome is the return of firefly season, that first early June night when the luminescent insects begin their flashing.
There are other such creatures in the world, but none quite like these. The U.S. has about 50 species, the tropics many more. All share the property of having a marvelous final segment or two of their soft bodies which is capable of lighting up with a pale radiance.
What is the secret of this cool green illumination? How do fireflies produce light without heat? Scientists have identified the chemicals luciferin, luciferase, and adenosine triphosphate at work, and there apparently has been progress in understanding the cold fire in recent years. But much of the mystery remains. We see it on the wing, the living lights of the fireflies putting out their marvelous messages in light to attract mates.
Glowworms are the wingless females of some firefly species. They signal to the airborne males above from among the stems of grass. Fireflies are not flies, but a kind of beetle.
The larvae live underground and in rotting wood or refuse. They eat tiny insects, as the adults probably do too — except for some kinds which may never eat at all once they become adults.
Early summer seems to be the optimum time for fireflies. In his book A Walk Through the Year, naturalist and entomologist Edwin Way Teale writes of a great display of fireflies observed by him and his wife in Connecticut on one June 21.
Teale goes on to say that fireflies seem most numerous in the air between about 10 P.m. and midnight, "on nights moist and warn." It seems many of us —Teale and I included — have looked up spellbound to see them intermingle with numerous stars in what were, therefore, rather non-humid nights. Is that point of light you see 60 feet or 60 light-years away? I'm pretty certain I've seen fireflies floating among the tops of 100-foot tall tees, but their distance can indeed be difficult to estimate.
I wonder if it was heat, humidity, or both which has set off displays of fast, seemingly wild and erratic flashing which I've seen in fireflies a few times when a thunderstorm was approaching. Could their strange behavior have been due to the charge in the air? From the ozone from lightning? But the storms had not arrived yet...
Or — is it possible? — were the little bugs reacting to the flashing from what their instincts mistook for a sky-wide firefly? Some people — my wife is one of them—grew up calling fireflies by one of their popular names: lightning bugs.
Surely everyone has caught a firefly in his or her hand and watched the pulsing glow shine out from within. We still often hear people encouraging kids to capture and keep as many of them as possible in jars. That may not be such a good idea. Of course, in some years and some places, the number of fireflies is stupendously large — in the year of Teale's memorable display he asked, "In this June night, who can guess how many billion fireflies are on wing above the dark fields of eastern Connecticut?"