When John Wallace was a kid, he saw the arrival of fireflies, blinking above the dewy grass at dusk, as the unofficial start of summer fun.
"We would collect hundreds in our little bug jugs and use them as lanterns for sleepouts, then turn them loose in the morning, only to go out on our lantern missions the next night," recalled Wallace, now a professor emeritus of biology at Pennsylvania's Millersville University.
Fireflies glowing to attract mates has been a wonder for generations. A new study has found that climate change, loss of habitat and light pollution affect their populations. (Carla Young)
That kind of wistful youthful memory resonates with millions of people, most of whom likely have been saddened to hear anecdotal reports that fireflies are declining throughout the Mid-Atlantic and other parts of the country.
Now, a study by researchers mostly from Penn State University concludes that habitat loss, and pesticides — as well as climate change — do indeed present a threat to at least some species of the glowing beetles. Artificial light is another disrupter, researchers say, because fireflies use species-specific flashes to attract mates. The research claims to be the most comprehensive yet on what influences firefly populations in the eastern U.S.
A blinking firefly rises. (David Hughes)
"Lights are problematic not just for adults flashing and trying to find [mates], but also for larvae," said Christina Grozinger, a professor of entomology at Penn State and senior author of the study. Larvae tend to burrow further underground when there's artificial light, she said, potentially impairing their development.
Another important problem is the loss of open ground to buildings, roads, parking lots and the like. Loss of pervious surfaces is pivotal because fireflies spend up to the first two years of their lives as larva on and under the ground.
Only in the last few weeks of their lives do they morph into the adult versions that blink their way to each other to mate on summer evenings, then lay eggs for the next generation.
One surprise in the study, which will appear in the June issue of Science of the Total Environment, is the growing import of climate change.
"An important implication from our model results is that climate change is likely a serious threat to North American firefly populations," the study concluded.
How?
How efficiently fireflies hibernate in the ground in winter, when they emerge to find mates and how long they survive in summer are all climate-dependent, researchers said. Weather fluctuations could throw off those ancient cues and trigger untimely releases of stored energy. Extreme rain could drown populations. Too much heat makes fireflies less active and less likely to find mates. Drought can make their larval homes in the soil unlivable.
"It is uncertain how firefly populations will be able to cope. In some places, habitat may become better. In others worse. But will fireflies be able to move to the new places? How far can they travel? Not much is known about dispersal of larvae or adults in most North American species," said Sarah Lower, assistant professor of biology at Bucknell University and a study co-author.
Fireflies dance at dusk at a firefly festival in Pennsylvania. (Peggy Butler)
The study concluded that in some regions of the country, conditions may even boost firefly populations, but species elsewhere could disappear altogether.
Lack of data makes it especially difficult to predict the future for fireflies; their populations and life cycles have simply not been monitored in detail.
About 170 species of fireflies are found in the U.S., in every state except Hawaii, but mostly east of the Rocky Mountains. The state insect of Pennsylvania is, in fact, a firefly — with the apt scientific name of Photuris pensylvanica — one of 30 known species in the state. But little research has been done on the status of individual species. Fireflies may seem plentiful in one area, but they may be a common species, while others are struggling.
An adult firefly flashes a unique sequence to attract a mate of its species. (Radim Schreiber/Fireflyexperience.org)
Researchers are beginning to get a handle on how some species are doing. When the International Union for Conservation of Nature examined 132 firefly species worldwide, it concluded that 28 were either threatened or in danger of extinction.
Yet, as an example of how scant reliable baseline information is, Christopher Heckscher, a Delaware State University professor looking for firefly species, fairly easily discovered four previously unknown species in Delaware, New Jersey and New York.
The study by Grozinger, et al., used a unique approach in its search to learn about factors that impact fireflies. The six researchers analyzed more than 24,000 firefly observations made by residents living east of the Mississippi between 2008 and 2016, as part of a citizen-science project known as Firefly Watch, now called Firefly Atlas.
Then the scientists dug up detailed information on the types of habitats, soil, weather conditions, amounts of artificial light and other factors of each observation. They were aided by artificial intelligence, remote sensing imagery and soil-type data.
Altogether, the study looked at 79 variables that could affect local firefly populations.
One hopeful finding for those living in rural areas of Pennsylvania, Maryland and Virginia is that farm fields are crucial habitat that allows large numbers of fireflies to find each other, even though potentially harmful pesticides are more likely to be present.
Insect-friendly conservation measures on the local level are important, researchers and firefly advocates say. Here are some actions they recommend.
- Keep part of your property unmowed or even grass-free. Leaf litter on top of bare soil is ideal habitat for the beetles.
- Don't use pesticides.
- Turn off outdoor lights during prime firefly mating season in June and July.
- Include a diversity of trees, shrubs and plants to provide cover and shade.
- Add a water feature.
To see fireflies fade to black would be a terrible blow to the country's collective consciousness, said Aaron Haines, a professor of biology at Millersville University.
"To lose them," he said, "would be to lose part of our identity."
Originally published on BayJournal.com.
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