Now is the time for the ultimate light show. I’m not talking about the fireworks that lit up the sky over the 4th, nor those gossamer curtains that dance across the heavens when sunspot activity is just right (although, I must say that northern lights are a real contender). No, I’m referring to fireflies, those dancing lights that must’ve been the inspiration for many a faerie legend.
First off, we must set the record straight: fireflies are not flies. They are beetles. It may be a small thing, but it is important that we start off on the right foot. Insects with hard wing covers are beetles. Fireflies have hard wing covers. Insects with two wings are flies. Fireflies have four wings: the two forewings are the wing covers, and beneath them are are the two delicate back wings. Still, to suddenly start calling them “firebeetles” would probably confuse a lot of folks, so we’ll stick with tradition and call them fireflies. (We could go with their alternate name, lightning bugs, but we run into the same problem: they are not bugs. Bugs are actually a specific Order of insects known as True Bugs. But I digress.)
So, you find yourself standing in your back yard on a balmy night in June or July. The sun has long set, and there above the grass, above the shrubs, you see a flash of light. Then another. A couple flashes glint from down in the grass. Some of the lights zigzag, others form an ephemeral “J”. Some go up, others go down. Some flash high in the air, some flash at medium height, and some flash close to the ground. Some flash all night, some flash for only a few minutes. The more you watch, the more variations you see. What does it all mean?
Perhaps it is best we start simply. Only male fireflies fly. Therefore, any flashing you see above the ground is a male firefly. The females do not fly (they don’t have wings), so they flash from the ground.
Now it gets more difficult, for there are many species of fireflies and each has its own flash pattern, which can vary in color, brightness and timing. Some species flash early in the night, while others prefer a later hour. Each species also claims a preferred height above the ground at which to make its display. If you learn all these characteristics, you are well on your way to knowing which fireflies like your yard.
Let’s take a look at a very common firefly, Photinus pyralis (sorry – they don’t have common names). You can recognize this firefly’s pattern easily: it is bright yellow and its flash is an upward rising light, forming a “J”. In the early part of the night, P. pyralis flashes close to the ground, but as the night progresses, he moves higher. He starts off by giving a set of flashes, each about six seconds apart (depending on the temperature; the warmer the night, the closer together the flashes will be). The female will respond with a flash about two seconds after the male flashes. If he sees this, he flies towards her, the two repeating their sequences until they meet.
After a tete-a-tete, the female will be off to lay her eggs (in some species the eggs glow), from which will emerge larvae that we call glowworms. The larvae lurk underground until spring, hunting voraciously for subterranean prey. Some species will stay as larvae for a second year. Anyway, come spring, they pupate and emerge as adults.
But what about that light? Where does it come from? Does it burn? The glow of the firefly is a natural light called biolumenesence. Biolumenesence is a cool light, meaning that the energy that is released in its making goes almost entirely into making light – little to no heat is produced. If only mankind could replicate this! In these insects the light is the result of a chemical reaction that takes place within the light organs on the underside of the abdomen. The firefly produces two of these chemicals: luciferin and luciferase. Added to these is ATP (adenosine triphosphate), a chemical that all living things have. The final ingredient is oxygen, which the firefly acquires through small openings along its abdomen. Once in contact these chemicals and voila! there is light. It’s like magic.
Seeing fireflies in your yard, catching fireflies in a jar, it’s a kind of rite of passage that every child should enjoy. This summer it seems like we have an abundance of fireflies, which is a wonderful thing. Some areas, though, are suffering a derth of fireflies. The southeastern US has seen a decline upwards of 70% in firefly populations. Biologists have been researching the cause for this, and light pollution seems to be the culprit. Street lights and house lights are huge contributors to this, but the new fad of solar lights along walkways and gardens seems to have been the “one straw too many.” Now even those dark(er) corners of yards have been lit up. With all this light, fireflies either a) don’t know it is night and therefore are not signaling for mates, or b) can’t see the lights of potential mates because they are overpowered by all the artificial lights man has turned on. If there is no mating taking place, there will be no future generations of fireflies.
It is a blessing to live in the Adirondacks, where we still have a fair bit of dark sky and can see the fireflies and stars before we go to bed.