Recently, while scooping up ‘toadpoles’ from the edge of the pond where marsh grasses, cattails, and bushes thrive, I had a conversation with my neighbor about some of the problems associated with people who left bright lights on all night around the lake. This woman missed the firefly display and was aware that light pollution was partially responsible for the loss of these beetles.
When I first moved to the mountains almost 40 years ago I camped in the field next to the brook and couldn’t fall sleep at night because it seemed as if the field itself was on fire with thousands of magical lights that blinked as they skimmed the tall grasses, glowing like gold or emerald jewels. For a naturalist like me, the season of summer began with the days of longest light, thunderstorms, and the advent of fireflies lighting up the night. The loss of so many ‘lightening bugs’ impoverishes us all.
Fireflies have been around since the dinosaur era; these extraordinary insects are at least a hundred million years old with one group spreading through this continent and the other colonized Europe and Asia. There used to be about 2000 species of these insects; now many are facing extinction.
Fireflies are winged beetles. A similar group of organisms are glowworms. The term “glowworm” can refer to firefly larva or wingless adult female fireflies. Both glowworms and fireflies are bioluminescent.
When a chemical called luciferin inside their abdomen/tail combines with oxygen, calcium and adenosine triphosphate, a chemical reaction occurs that results in bioluminescence. This ‘cool’ light is the most efficient in the world because almost 100 percent of the energy used is emitted as light and not heat.
Each species uses it own pattern of lightening flashes to attract a mate, and most fascinating is that some fireflies synchronize their yellow, pale red, green, or orange lights. Several studies have shown that female fireflies choose mates depending upon specific male flash pattern characteristics. Higher male flash rates, as well as increased flash intensity, have been shown to be more attractive to females in two different firefly species.
Some Scientists believe fireflies and their larvae glow to warn predators that they are toxic. Many would be predators are repelled by firefly blood that contains defensives steroids which apparently taste awful!
Adults typically live less than a month, but their larvae live up to two years, so it’s primarily threats to larvae that threaten the beetles.
Some firefly larvae can emit light from underground, and in some species the eggs glow. The underground-dwelling larvae of the lightning bug are carnivorous and feast on slimy slugs, worms and snails. Others live in the water, have gills and eat aquatic snails before coming ashore. Most adult fireflies feast on pollen and nectar.
Fireflies thrive as larvae in rotting wood and forest litter at the margins of ponds and streams. And as they grow, they more or less stay where they were born. Some species are more aquatic than others, and a few are found in more arid areas—but most are found in fields, forests and marshes. Their environment of choice is warm, humid and near standing water of some kind—ponds, streams and rivers, or even shallow depressions that retain water longer than the surrounding ground.
Both male and female fireflies use their flashing lights to communicate. All species speak a language of light.
Human induced artificial light pollution (including those cute little solar lights) interrupt firefly flash patterns. Scientists have observed that synchronous fireflies get out of synch for a few minutes after a car’s headlights pass. Light from homes, cars, stores, and streetlights may make it difficult for fireflies to signal each other during mating—meaning fewer firefly larvae are born next season. Where fireflies once had uninterrupted forests and fields to live and mate, homes with landscaped lawns and lots of exterior lights are now the norm.
Light can make them lose track of the time or their position. The fireflies may struggle to recognize important objects, such as their snail prey. In species where one sex is attracted to the glow of the other, artificial lights may disrupt mating. Finally, really bright lights may dazzle or even blind the fireflies.
Fireflies display during warm summer evenings. If there’s a lot of background illumination from artificial light, then their signals are going to be less visible. Additionally, fireflies’ eyes are particularly sensitive to certain kinds of artificial light. One study of the eyes of British glow-worms revealed that the male’s eyes were tuned to the females’ green light but when blue light was added the males couldn’t find the females. This means that the bluish LED lights are more likely to disrupt the fireflies’ ability to find mates.
Another factor in firefly disappearance is habitat loss. When fields are paved over fireflies don’t migrate; they simply disappear, suggesting that these insects like so many wild creatures are tied to a particular place. The fireflies of Southeast Asia are another example. The males have flashing lights with which they attract females. They gather at night in mangrove trees lighting up the night. The females fly in and choose their mates. In some species the males synchronize their flashes, creating spectacular displays that tourists travel great distances to witness. Most of these fireflies live only around riverbanks. After mating, the females lay their eggs in the mud. The larvae develop in the banks and spend months feeding on snails before becoming adults and returning to their display trees. All the parts of their life-cycle depend on that habitat which is currently being destroyed by logging.
Common glow-worms face many of the same threats as other fireflies, but are particularly vulnerable because adult females cannot fly. They have difficulty colonizing new sites, or recolonizing sites after they have been lost,
Pesticides are another major threat. Most of a firefly’s life is spent as a larva, on or under the ground, or underwater. There, they are exposed to pesticides like DEET whose poison lingers in aquatic environments. Firefly larvae are especially at risk because they are predators, normally hunting small snails, each of which may contain a dose of pesticide. Adults also have specialized diets, so they can die or starve to death if their food supply is contaminated or absent.
There are so many things we can do to help restore our dwindling firefly populations. First, we can turn of our outside lights unless we are actually using them. We can also mow our lawns less frequently, or better yet, shrink or replace those lawns with native grasses, plants, flowers and mosses. We can also leave piles of leaf litter around the edges of our open land as I do here. We can also reduce the amount of ground disturbance by allowing wild plants to grow naturally around the forest edges like the wild lily of the valley and the ferns that are so abundant in this area. It is unrealistic to ask people not to use DEET when the threat of Lyme disease is so dire, but we can learn to use it safely. I go into my garage and shut the door before spraying my sneakers and socks. Hopefully, most of us have eliminated chemical fertilizers and pesticides like Round – Up which are deadly to all insects, animals, and birds.
I don’t know about you but I don’t want to think about a world without fireflies for they offer us the gift of wonder, while creating a place in our hearts to fall in love with nature all over again every single summer.