Firefly populations face multiple threats across North America

A groundbreaking study has brought new insights into the factors impacting firefly populations across North America. By leveraging extensive citizen science data and advanced analytics, the experts unpacked the environmental and human influences on these beloved insects.

The study was conducted by researchers at the University of Kentucky, Bucknell University, the Pennsylvania State University, and the US Department of Agriculture (USDA).

Identifying threats to firefly populations 

“As insect populations decline in many regions, conservation biologists are increasingly tasked with identifying factors that threaten insect species and developing effective strategies for their conservation. One insect group of global conservation concern are fireflies (Coleoptera: Lampyridae),” wrote the study authors. 

“Although quantitative data on firefly populations are lacking for most species, anecdotal reports suggest that some firefly populations have declined in recent decades.”

“Researchers have hypothesized that North American firefly populations are most threatened by habitat loss, pesticide use, and light pollution, but the importance of these factors in shaping firefly populations has not been rigorously examined at broad spatial scales.”

Integrating large scale data sets 

The research, utilizing over 24,000 surveys from the Firefly Watch citizen science initiative, represents the first comprehensive effort to apply a data-driven approach to understand firefly population dynamics across a vast geographic scale. 

“Subtle changes in climate patterns, especially related to temperature, are significantly impacting firefly breeding cycles and habitat quality,” said study lead author Darin McNeil, an assistant professor of wildlife ecology and management at the University of Kentucky.

“In this study, we integrated large scale data sets on species abundance, land use, soil type, weather and climate using machine learning models to precisely model and predict firefly abundance patterns at the local scale across the eastern U.S. We were very fortunate to have a multi-year citizen science data set that spanned more than 24,000 observations,” noted study senior author Christina Grozinger, a professor of entomology at Penn State.

Climate change, light pollution, and agriculture 

The findings highlight the vulnerability of fireflies to climatic variables such as temperature and precipitation. Since fireflies thrive in temperate conditions, with wet and warm summers providing ideal breeding environments and cold winters supporting the survival of immature stages, climate changes are likely to be highly challenging.

Moreover, the scientists found that urban growth and light pollution can negatively impact this species. “Artificial lights at night could disrupt firefly populations, possibly affecting both adult and larval stages,” McNeil said. “Firefly larvae, which live in the soil, are particularly vulnerable to changes in light exposure and artificial light could alter their developmental cycles and survival rates.”

The researchers also investigated the impact of agricultural practices. While they did not find a direct pesticide effect, they discovered that certain agricultural areas supported some of the highest firefly densities, possibly due to practices like livestock grazing that create favorable meadow-like conditions. However, the scientists cautioned against the intensification of agriculture that could diminish the organic debris and moist environments essential for firefly larvae.

Long-term trends in firefly populations 

“As the study concludes, further research is encouraged, particularly in exploring the long-term trends of firefly populations and the efficacy of various conservation strategies. Moving forward, focused studies that survey particular firefly species, rather than the firefly community as a whole, will be important,” McNeil said.

“Each individual species has its own habitat requirement and things it needs to succeed. With the citizen science data in this study, we’re looking at fireflies in the aggregate, but we would like people in citizen science getting more training in species identification. If we can get species-level information, we can provide more specifics on species living in a particular area and how best to protect them,” added co-author Sarah Lower, an assistant professor of biology at Bucknell University.

To gather comparable data for different firefly species, the research team is utilizing technology and artificial intelligence to establish automated monitoring systems. This initiative is part of an NSF-funded INSECT NET graduate training program designed to enhance the precision and reach of ecological studies.

For individuals keen on understanding the land use, weather, and climate specifics of their areas, Penn State offers the Beescape tool. This online resource delivers tailored habitat quality scores for pollinators, helping users assess and improve local conditions for these vital creatures.

The study is published in the journal Science of the Total Environment.

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