Moths and Fireflies Are Declining As Summer Night InsectsJun 30, 2023 ● By Sheryl DeVore
John James Audubon illustrated the whip-poor-will with its main food, moths. Courtesy National Gallery of Art, Washington/Public domain.
As the summer sun sets, butterflies cease patrolling flowers for nectar, go to roost and rest. But many moth species are just beginning their day under the cover of darkness, and nighttime active birds called whip-poor-wills come out to eat these insects.
Unfortunately, insect numbers have been declining worldwide, and according to the National Audubon Society, numbers of some nighttime active birds such as whip-poor-wills are also decreasing because they cannot find enough large moths to eat. These birds are among other species such as common nighthawks in the Chicago area that rely on a strong population of moths and moth larvae for food.
Illinois researchers discovered that whip-poor-wills are more common in areas where large moths are available. Ian Souza-Cole writes in a paper published in the journal Ornithological Applications that “Eastern whip-poor-will abundance declines with urban land cover and increases with moth abundance in the American Midwest.” He says that whip-poor-wills prefer living along forest edges during the summer in Illinois, “but only when the edges were associated with high moth abundances.”
“With insects and many types of organisms, you get a day shift and a night shift,” says Doug Taron, chief curator emeritus at Peggy Notebaert Nature Museum, in Chicago. “Most people pay attention to the day shift.” Taron also pays attention to the night shift. In summer, he turns on the light next to his screened porch at dusk. Moths, attracted to the light, land on the screen.
“One of the most interesting groups of moths I sometimes get at the screen are known as the underwing moths,” Taron says. “Their wings are patterned like tree bark and they spend the day camouflaged in trees. When they come out at night, if a predator approaches, this group of moths lifts forewings to expose a bright color such as yellow or red. The startling flash of color may frighten the predator.”
“Not all moths are nocturnal, but from an evolutionary perspective, the moth may have come before the butterfly,” Taron says. Moths and butterflies are part of the large Lepidoptera order of insects. Many more species of moth compared with butterflies exist. Moths likely appeared on the Earth 300 million years ago, and butterflies evolved from some of the day-flying moths. In general, a new group of moth species emerges about every two weeks during the year, with midsummer the peak for species diversity and abundance. Some 1,850 species of moths exist in Illinois. These include a large group of sphinx moths, some of which resemble small hummingbirds as they stick their long tongues into a flower’s corolla for nectar.
Both moths and butterflies function as the bottom of the food chain to help recycle nutrients into the earth. A caterpillar feeds on plant leaves. Birds eat caterpillars and gain the energy from the plant leaves. The caterpillars of butterflies and moths are often nocturnal, eating their meals at night.
Researchers have shown that it may take 6,000 to 9,000 caterpillars to rear one chickadee family. Through research in Washington, D.C., entomologist and author Douglas W. Tallamy discovered most of the caterpillars chickadees ate were moth species attracted to native plants. “Adding even a few native plant species to your yard can benefit a multitude of these valuable invertebrates,” writes Jim Steffen, at the Chicago Botanic Garden. Steffen, who retired in 2021 as a senior ecologist, studied moths at a restored oak woodland and found roughly 600 species of moths.
A good time to see moths is in late summer, when they visit blooming native prairie plants, Taron says. He visits his blooming tall coreopsis at dusk in late summer and often discovers small, brown moths sipping nectar. These moths belong to a large group of organisms called inchworms. “There are bunch of species you can see on tall coreopsis in the summer when it’s in bloom,” he says. Although in general, moths tend to be duller-colored than their daytime counterparts, the butterflies, several moth species in the region are quite beautiful; for example, the polyphemus moth, a type of silk moth, and the cecropia moth. “It’s usually a random encounter with these species, because they’re mostly nocturnal,” he notes.
“Many years ago, when I was working at the museum, someone called to say they had found a large moth, and the description (monarch-sized, brown, with big blue and yellow spots on the hindwings) was adequate enough to call it a polyphemus. The caller wanted to know if he could keep it in an aquarium overnight and show his daughter in the morning,” recalls Taron. He said that would be fine as long as it got released soon after. When the daughter arrived, there were a dozen other polyphemus moths fluttering around the aquarium. “It turned out the moth was a female and she was emitting pheromones,” he says. The moths fluttering outside were males, and that’s how they find mates in the dark—by following the powerful pheromones. “What a wonderful experience to share with his daughter. It’s always wonderful. There is a certain special quality to seeing moths that you don’t see as easily as butterflies.”
Taron recalls seeing a luna moth, large and luminescent green, being attracted to floodlight at his parents’ deck in the dark when he was in junior high school. “It looked like a bird flying around,” he remembers.
The most frequently seen nighttime insect in July is likely the firefly, or lightning bug, which is vulnerable to the same issues as other insect species, including habitat loss and use of pesticides, according to Taron. More than 120 different firefly species live in North America, and likely several different species are glowing in suburban yards in July and August. Though numbers of fireflies can vary from year to year, the Xerces Society for Invertebrate Conservation says one in three North American firefly species may be at risk of extinction.
In spring, firefly larvae or caterpillars turn into pupae and then emerge as adults. Males take short flights and emit flashes to attract females, which flash back to accept the male. After mating, the female lays eggs in moist soil, on a dead log or in moss, which hatch and overwinter as larvae. Fireflies flash patterns and variable glow colors to help distinguish the species so they can find the right mate. As larvae, these insects eat earthworms, snails and slugs. As adults, they drink nectar and eat other insects, including other species of fireflies. The light they emit occurs when a reaction among chemicals in the fly’s abdomen converts chemical energy to light energy, not heat.
Taron says he enjoys looking for juvenile fireflies in late summer. Called glow worms because they also emit light at night, the firefly larvae look “almost prehistoric,” he says. “One thing helpful to fireflies is to not keep your garden so tidy.” In other words, mow higher and less frequently, and avoid using insecticides. “Keeping the grass longer and wetter will protect the millipedes and snails that firefly larvae feed on,” he explains.
Sheryl DeVore has written six books on science, health and nature, as well as nature, health and environment stories for national and regional publications. Read more at SherylDeVore.Wordpress.com.
Field Guide to Silk Moths of Illinois, by John K. Bouseman and James G. Sternburg.
Field Guide to the Sphinx Moths
of Illinois, by James R. Wiker, James G. Sternburg and John K. Bouseman.
A Beginner’s Guide to Moths of the Midwest, by Angella Moorehouse.