I remember walking across a parking lot to my car early one morning about 20 years ago. Under a streetlight was a pile of dead moths, looking a bit like a tiny pile of snow. I was tempted to take a snow shovel and heave away the heap of wings and bodies.
That evening, I saw yet another swarm of moths fluttering under a streetlight. There seemed to be no end. No matter how many moths died, or were distracted from eating or reproducing, every night there were still more of them circling the streetlight. I remember thinking that the number of moths in the world must be virtually infinite.
At about the same time I was pondering the pile of dead moths in the parking lot, Kenneth D. Frank, a medical doctor based in Philadelphia who studies moths as a hobby, was putting together information on the impact of outdoor lighting on moths.
What he found was not surprising. Some species of moths are strongly attracted to light. Some are not attracted to light at all. For those that are, outdoor lights both distract them from eating and reproducing and make them more vulnerable to predators, including bats and spiders.
Frank found that moths get fried on the hot bulbs and are more likely to be hit by cars when they tarry in the roadway under streetlights. He also found that when moths spend the day near that very attractive light, perhaps on the wall of a building, they are not camouflaged the way they would be if they were resting on a tree. Areas around artificial lights are like bird feeders, he found.
That scientific paper, published in the 1980s, was one of the first to detail the effects of artificial night lighting on animals. Perhaps the ecological study of artificial light would have taken off faster if that pioneering paper had been done on a more popular creature; after all, moths eat our sweaters, invade our pantries, cut down our seedlings (cutworms), destroy the cabbages and broccoli in our gardens (cabbage loopers), and defoliate our trees (tent caterpillars).
But moths play a vital role in natural systems wherever they occur. Birds and bats eat adult moths. Most every creature that eats other creatures also eats caterpillars - birds, turtles, spiders, lizards and more. Caterpillars are a sort of hamburger to the world, said University of Pennsylvania scientist Dan Janzen on the radio show “Pulse of the Planet.” While butterflies also live as caterpillars in their larval stage, moths far outnumber butterflies overall, meaning that your typical caterpillar is on its way to becoming a moth.
Despite their reputation for being drab, some moths are quite beautiful, particularly the native giant silk moths. For example, cecropia moths, which are found in our area, are huge, with up to six-inch wingspans. Their wings are dark brown, accented with a red and white band. Their wings have white crescent spots that look like phases of the moon, and their bodies look as though they are red and white striped.
Because there are just so many moths, and because we know so little about these creatures of the night, no one is sure what the status of moth populations in the United States are.
In Britain, though, scientific studies have turned up some bad news. Last year, a report released by a British organization called Butterfly Conservation showed that the number of common moths in that country had fallen by a third since 1968. Of the 337 moth species studied, two-thirds of them showed a decrease in population over 35 years.
The report says that habitat loss, pesticides, over-use of fertilizers, light pollution and climate change are all likely suspects in the decline. Scientists have cited similar threats to important insects such as moths, butterflies, and bees in this country too, with light pollution being a hazard only to the night-flying moths.
Frank says that artificial night lighting might be playing less of a role today in the decline of moths than it did 20 years ago, ironically because there is so much more of it. “Flight- to-light behavior seems to be triggered by the contrast between a lamp and the darkness surrounding it,” he explains. That means a lonely light over a barn door attracts lots of moths. A brightly lit highway strip of big-box stores attracts few moths.
The best science says that we don’t have enough information to know what is happening for sure, although the signs point toward moth decline. Perhaps there are two factors at work: fewer moths flapping around the average porch light, and fewer of the big, beautiful, native giant silk moths around to grab the attention of casual observers, says Frank. Moths are fading from the public eye even as they fade from our environment.