Illuminating patterns of firefly abundance using citizen science data and machine learning models

Authors: MCNEIL, DARIN - University Of Kentucky; Goslee, Sarah; KAMMERER, MELANIE - Oak Ridge Institute For Science And Education (ORISE); LOWER, SARAH - Bucknell University; TOOKER, JOHN - Pennsylvania State University; GROZINGER, CHRISTINA - Pennsylvania State University

Submitted to: Science of the Total Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/6/2024
Publication Date: 4/10/2024
Citation: McNeil, D.J., Goslee, S.C., Kammerer, M., Lower, S.E., Tooker, J.F., Grozinger, C.M. 2024. Illuminating patterns of firefly abundance using citizen science data and machine learning models. Science of the Total Environment. 929:172329. https://doi.org/10.1016/j.scitotenv.2024.172329.
DOI: https://doi.org/10.1016/j.scitotenv.2024.172329

Interpretive Summary: Fireflies are an appealing summer sight in the eastern United States, and firefly larvae are also predators of snails and slugs in croplands. Fireflies, like many other kinds of insects, have been reported to be declining in abundance, but it is uncertain how habitat loss, climate change, and other possible causes relate to these declines. We used long-term Firefly Watch data from 2008-2018 and machine learning models to investigate the importance of potential multiple drivers of firefly distribution and abundance. Weather and climate were highly important, but interacted with land use and soil type. Firefly conservation strategies will need to incorporate multiple types of practices to maintain this charismatic insect.

Technical Abstract: As insect populations decline in many regions, conservation biologists are increasingly tasked with identifying the factors that threaten insect species and developing effective strategies for insect conservation. One insect group of global conservation concern are fireflies (Coleoptera: Lampyridae). Many firefly species are highly charismatic as adults because of their bioluminescent courtship behaviors, but their soil-dwelling larvae also provide valuable ecosystem services as predators of agricultural pests (e.g., snails and slugs). 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. Using data from >24,000 surveys (spanning 2008-16) from the citizen science program Firefly Watch, we trained machine learning models to evaluate the relative importance of a variety of factors on bioluminescent firefly populations: pesticides, artificial lights at night, land cover, soil/topography, short-term weather, and long-term climate. Our analyses revealed that firefly abundance was driven by complex interactions among soil conditions (e.g., percent sand composition), climate/weather (e.g., growing degree days), and land cover characteristics (e.g., percent agriculture and impervious cover). Given the significant impact that climactic and weather conditions have on firefly abundance, there is a strong likelihood that firefly populations will be impacted by climate change, with some regions becoming higher quality and others potentially losing firefly populations altogether. Collectively, our results support hypotheses related to factors threatening firefly populations (especially habitat loss) but suggests that climate change may pose a greater threat than previously appreciated. Thus, future conservation of North American firefly populations will be reliant upon 1) consistent and continued monitoring of populations via programs like Firefly Watch; 2) efforts to mitigate the impacts of climate change; and 3) insect-friendly conservation practices that minimize the extent of impervious cover and maintain access to the soil surface.