From droppings to data: eDNA metabarcoding for use in insect monitoring

Insect biodiversity is declining at alarming rates, yet existing monitoring methods are often labor-intensive, taxonomically limited, and poorly scalable. Environmental DNA (eDNA)—genetic material shed by organisms into their environment—and metabarcoding—a method that uses high-throughput sequencing to identify multiple species from mixed DNA samples—have emerged as transformative tools for biodiversity assessment, offering non-invasive, efficient, and taxonomically broad approaches to detecting insect communities. Here, we examine how frass—once used primarily by entomologists to estimate biomass—can now serve as a valuable eDNA source for assessing species richness within insect communities. Over the course of a year, frass was passively collected on a weekly basis from nine sites spanning an urbanization gradient and analyzed using Lepidoptera-specific metabarcoding to identify caterpillar community composition. Preliminary findings suggest a weak decline in overall caterpillar biomass with increasing urbanization. Still, we hypothesize this pattern masks community-level shifts: a dominance of urban-adapted generalists in developed areas, and a greater richness of specialist species in rural habitats. This frass-based eDNA method not only offers insight into how moth communities respond to urbanization but also represents a scalable tool for conservation monitoring, a tool that is becoming more accessible and powerful for insect biomonitoring studies.