Fireflies are often associated with warm summer nights, lighting up backyards and fields, yet many species are habitat specialists found in wetland or forest habitats. Some firefly species–particularly the specialists–are experiencing declines due to a variety of threats including habitat loss, light pollution, climate change, and pesticide exposure. While we know there are varying degrees of impact, we lack species-specific data on how individual threats affect firefly populations. And these aren’t the only threats impacting firefly populations. An additional threat that gets less attention in the firefly world is invasive species. Invasive plants can alter a habitat’s composition, ecosystem function, and hydrology, creating a monoculture that negatively impacts firefly populations. Invasive animals may compete for resources, occupy habitat niches displacing native species, or introduce parasites or disease.
They may even change the structure of the habitat itself. Take, for example, the earthworm. Earthworms are a familiar group of animals, and while they seem like simple creatures, they have a complicated story. You’ve probably heard that earthworms are beneficial in agricultural and garden settings because of their role as decomposers, turning organic material into rich soil. But these ecosystem services are only helpful in areas where they naturally occur. Large swathes of the US that underwent periods of glaciation, like many temperate northern forests, lack native worms. Because these communities evolved without earthworms, their introduction can be damaging. Several earthworm species from Europe and Asia can now be found throughout northern temperate forests in North America.
This isn’t to say that all worms are problematic. Native earthworms (totaling over 100 species) are present in many unglaciated areas of the United States, including parts of the Pacific Northwest and the South. These native species have interesting life histories and play important ecological roles in their natural communities. Some, like fireflies, are even bioluminescent.
Are introduced earthworms an issue for northern temperate forests? Where do fireflies come in?
While earthworms serve as a food source for a variety of wildlife, they are also environmental engineers altering the natural community. Some earthworms consume and turn over leaf litter so quickly that the duff layer (the built-up leaf litter) that plants and animals have evolved to rely on is degraded or lost. This may not be an issue in places where native species have evolved alongside the rest of the plant and animal community. But the establishment of invasive worms can cause severe changes to the forest floor, herbaceous layer, and other microhabitats, resulting in declining forest health and drier soils.
Fireflies rely on moist conditions, especially in the larval stage when they are prone to desiccation (drying out). Ideal habitat conditions often include a lush understory with a diversity of herbaceous vegetation and thick leaf litter, creating moist environments for larvae and their prey. Introduced worms put leaf litter at risk. Their consumption of leaf litter–natural and heralded in some settings–can quickly alter the forest floor, changing conditions for fireflies and other wildlife and plants.
Could earthworms benefit fireflies?
On the other hand, more earthworms could be a good thing for fireflies–after all, they’re a food source. The firefly larval stage, which lasts for approximately 1-2 years, is dedicated to eating, and earthworms and other soft-bodied invertebrates like caterpillars, snails, and slugs make up a large part of their diet. Some firefly groups have food preferences. For example, species in the genus Pyractomena tend to prefer snail prey, whereas species in the genus Photuris are generalists and consume everything including earthworms. True earthworm specialists are not well known in the U.S. or Canada, although they have been reported from other regions of the world, particularly in Southeast Asia (e.g., Stenocladius bicoloripes, Diaphanes citrinus, and D. lampyroides). That said, because larvae in the genus Photinus are subterranean, we suspect earthworms may make up a decent part of their diet.
We need more research on the relationships between worms and fireflies.
Research into larval firefly diets is limited, and more studies are needed to understand which firefly species in the U.S. and Canada rely on worms as integral parts of their diets. In addition, we need a better understanding of how invasive worms impact fireflies and their habitats. The relationship between forest health, firefly populations, and invasive worms is complex. The presence of invasive worms could negatively impact habitat quality while simultaneously serving as a food source for many firefly species. Questions that merit further investigation include:
- Do healthy firefly populations help keep earthworm populations in check, resulting in higher quality habitat?
- Are firefly larvae of various types (Photinus and Photuris) able to prey upon invasive jumping worms (Amynthas spp.)?
- Does the presence of earthworms support healthy firefly populations by serving as an important food source?
- Do earthworms, which are very efficient decomposers, change forest floor conditions in such a way that it becomes unsuitable for firefly populations and other invertebrates?
- Do bare forest floors lead to fewer earthworm predators and a boom in earthworm populations, amplifying the negative impacts on forest health and tree vigor?
What can you do to support forest health?
Invasive worms spread into new areas via mulch, compost, and potted plants; in soil on tools, equipment, and shoes; and in soil runoff. You can help keep forests healthy for fireflies and other wildlife by:
- Nurturing soil health with native plants, natural leaf litter, and decomposing wood
- Monitoring your yard or local natural areas for invasive worms and reporting what you find to your local extension office or citizen science projects such as:
- Buying mulch, compost, soil, and plants from certified sources
- Refraining from moving soil and plants around from one site to another
- Washing your yard and garden supplies before using them in a different area
- Teaching others how to identify and report invasive worms
Learn more
Xerces Bug Banter podcast: The Underground Heroes: Earthworms
- Includes a discussion of how to avoid spreading invasive worms and how to support native species.
Xerces Pocket ID Guide to Invertebrates of Urban Soils
- Includes a section on common introduced earthworms and how to identify them
Further reading
Bal, T.L., M.E. Anderson, M.E. Brady, J.I. Burton, and C.R. Webster. (2025). Decadal changes in ground-layer plant communities reflect maple dieback and earthworm invasion in National Forests in the Lake Superior Region, USA. Forests. 16: 1583. https://doi.org/10.3390/f16101583
Bohlen, P.J., S. Scheu, C.M. Hale, M.A. McLean, S. Migge, P.M. Groffman, and D. Parkinson. (2004). Non-native invasive earthworms as agents of change in northern temperate forests. Frontiers in Ecology and the Environment. 2: 427-435. https://doi.org/10.1890/1540-9295(2004)002[0427:NIEAAO]2.0.CO;2
Faust, L.F. (2017). Fireflies, Glow-worms, and Lightning Bugs: Identification and Natural History of the Fireflies of the Eastern and Central United States and Canada. University of Georgia Press. Athens, GA. 356 pp.
Fu, X., and V.B. Meyer-Rochow. (2012). An investigation into the morphological and behavioral adaptations of the aquatic larvae of Aquatica leii (Coleoptera: Lampyridae) to prey upon freshwater snails that serve as intermediate hosts for the liver fluke. Biological Control. http:// dx.doi.org/10.1016/j.biocontrol.2011.12.007
