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Green and Growing: Where did all the fireflies go?

Fireflies, the little “jewels of the night,” were a big event at Fourth of July picnics during my western Pennsylvania childhood.

Our pack of cousins and siblings ran and yelped through the swarms after dark. Fireflies don’t bite, sting, or make noise, so no one stopped us from chasing the tiny lights while adults picked up the day’s picnic and packed the family automobiles.

Fireflies were so numerous, and they could brighten the night. Little did we know that the lights, a product of the insect’s “bioluminescence,” were key to their courting ritual. The aerial dance ensured fireflies would flash again next year.

These insects are no longer so numerous. My children grew up without experiencing the density of lights I saw as a child. An acquaintance of my age recently pined: Where have all the fireflies gone?

Dr. Gale Ridge, an entomologist at the Connecticut Agricultural Experiment Station, said that just as some are concerned with the decline of monarch butterflies, “Fireflies, which are beetles, might also be considered canaries in the coalmine. Fireflies are not immune to environmental degradation, and their numbers are declining.”

“Firefly larva hunt slugs, snails and earthworms,” she said. “They may help battle a newly invasive earthworm called the crazy snake worm. Thus, in part, they are not only charismatic but are also beneficial insects.”

Fireflies have also played leading roles in some biomedical research, including the detection of blood clots, tumors and food contamination, among other scientific inquiries.

In 2019, the Xerces Society for Invertebrate Conservation published an extensive report on the state of firefly survival titled “Conserving the Jewels of the Night,” available at bit.ly/Jewels-of-the-Night.

Fireflies are beetles, the report explains, and there are many species. According to Xerces’ estimates, Southern New England alone hosts 15 to 20 native fireflies.

“Fireflies are associated with a wide range of habitats,” says the report, “yet they all seem to have one element in common: moisture.”

After mating, females lay their eggs in moist soil, duff, leaf litter, or rotting wood. They spend up to two years as larvae, relying on the same wet, undisturbed habitat where adults lay eggs. “In general, most firefly species depend on moist habitats, including wetlands, streams and damp fields,” according to the Xerces report.

Furthermore, in northern climates, they go underground for the winter. Leaf blowers, lawnmowers, and loss of forested edges work against their survival. Pesticides, too, threaten fireflies. These beetles occupy many of the same habitats as mosquitoes, which are, these days, sometimes the target of spraying regimes. Fireflies’ prey — the soft-bodied slugs and snails they consume in vast numbers — are also vulnerable to pesticides.

Another problem impedes fireflies: artificial light at night. Research shows that bright night lights confuse male fireflies, making it challenging to find receptive females during their early summer mating season. Night lighting, in effect, reduces the number of eggs and larva they can produce.

The Xerces report offers a variety of antidotes for those who want their grandchildren and great-grandchildren to experience firefly magic.

First, they point out that long-term monitoring studies of fireflies are sparse. They recommend joining a citizen-scientist effort, such as the Fireflyers International Network’s project on iNaturalist, available at bit.ly/fireflyers.

Second, the Xerces team echoes advice given by many other groups: leave the leaves. Leaf litter, and the moisture it protects, is key to firefly survival.

Avoid soil disturbance in wetland areas and forests, whether by digging or driving machinery. Learn how to build or enhance firefly habitat at bit.ly/firefly-habitat.

As for pesticides, the report says, “Eliminate all cosmetic or unnecessary pesticide use that is not responding to economic damage or a public health risk.”

Finally, turn down the outdoor lights. “Being thoughtful about outdoor lighting will benefit not only fireflies but other nocturnal animals as well,” the report advises. Learn about lighting recommendations from the International Dark Sky Association at darksky.org.

Ridge offers the ultimate reason to care about fireflies and all insects.

“Insects are the workhorses for life on earth,” she said. “Sadly, if you lose the insects, you lose life as we know it on earth.”

Kathy Connolly is an Old Saybrook landscape designer who writes about horticulture and ecology. She can be reached through her website, speakingoflandscapes.com.

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