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Fireflies can bring magic to summer nights — blinking in yards and putting on light shows in fields. But a study by a team that includes researchers from Penn State found that while fireflies’ overall populations did not decline, climate change and loss of habitat do have an impact on the winged beetles. 

Christina Grozinger, Publius Vergilius Maro Professor of Entomology and director of the Insect Biodiversity Center in Penn State’s College of Agricultural Sciences, said the research team did not see overall declines in firefly populations, but did find differences in where and when fireflies do well.

“What we found was that there are some ecological regions and eco-climate patterns that are good for fireflies. And so for example, like warm summers, and cool winters are good for fireflies,” Grozinger said.

Lots of pavement and nighttime light pollution, on the other hand, are bad for the insects.

The study includes eight years’ worth of data from the eastern United States — from 2008 to 2016, with 24,000 observations recorded by citizen scientists in Firefly Watch. To crunch the huge datasets, the researchers used machine learning.

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Grozinger said fluctuating weather patterns, like those seen in Pennsylvania this year, can affect firefly populations from one year to the next.

“You can end up with years where you have very few fireflies, and then that makes people very concerned,” she said. “But, you know, if you come back to sort of better conditions the following year, then those populations can rebound.”

Lightning bugs live in soil as larvae. They eat snails and slugs.

“So they’re important in their own right for biological control and part of food webs,” Grozinger said. “And then they’re also indicator species of how good your habitat is for supporting insects and wildlife.”

Areas with dry soil or where there’s a lot of pavement are not good for them. 

“So if you have drier soils, or you are in an area where there’s a lot of sidewalks and parking lots and not soil for them, that’s not good,” Grozinger said. 

Artificial lighting also has a negative impact on fireflies. Still, Grozinger said, there are steps you can take to support their populations.

“So keeping nighttime lights low, making sure that there’s area for them to lay their eggs in and their larvae to do well in, and then having diverse vegetation in your area because they like the meadows to be able to — this is where they fly as adults and find mates, but they also like to be around tree lines,” she said. “So having trees with open landscaping is also really great for fireflies.”

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