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07/08/2020 07:00 AMFireflies, 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 that 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 insured fireflies would flash again next year.
These insects are no longer so numerous. My children grew up without experiencing the same 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, says that just as some are concerned with the decline of monarch butterflies, “Fireflies, which are beetles, might also be considered canaries in the coal mine. Fireflies are not immune to environmental degradation, and their numbers are declining.”
She says, “Firefly larva hunt slugs, snails, and earthworms. 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.”
Lights at Night Harmful
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.” (Free download at bit.ly/Jewels-of-the-Night.)
The darkness of night is important to fireflies, according to a report from the Xerces Society for Invertebrate Conservation, because males fireflies emit a particular flash pattern. Females generally do not fly, but instead, perch on low vegetation or the ground. If a female is interested, she will respond to the male by flashing back. This flash dialog can continue for more than an hour until the male finally locates the female.
Night lighting can interrupt male fireflies’ attempts to locate females. Furthermore, females cannot fly to males.
Artificial light at night (ALAN) is a problem for fireflies. 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.
Firefly adults are out and about during June and July. The adults live only about four days, but larvae live for as much as two years in leaf litter and other natural habitats.
Fireflies are beetles, the report explains, and there many species. According to Xerces’ estimates, Southern New England alone hosts between 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.
In addition, 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.
How to Help
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. The group’s goals include “to bring together people involved in firefly conservation and research around the world to exchange knowledge and form collaborative partnerships; to raise awareness and advance a public conservation ethic by sharing information about fireflies and their habitat requirements; and too foster delight and appreciation of fireflies across different cultures by blending artistic and scientific perspectives.” More information is 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 from Firefly.org: bit.ly/firefly-habitat. Tips include collecting bags of leaves to make “bag compost,” putting the bags, wet, in a shady lawn area to help attract slugs and snails, and then, in the spring, putting the bag compost in your garden.
“Repeat each year. It might take as long as 5 years, or as quick as that same year, to get fireflies in your garden.”
Other tips include planting trees and native grasses, and enriching your soil with leaves and other organic matter.
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. https://www.darksky.org/
Dr. Gale Ridge offers the ultimate reason to care about fireflies and all insects. “Insects are the workhorses for life on earth. 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. Reach her through her website, www.SpeakingofLandscapes.com