Nuisance status of a net-spinning caddisfly (Trichoptera: Hydropsychidae): Survey responses of residents on the Colorado River in Bullhead City, Arizona.

Municipalities on the lower Colorado River are seasonally overwhelmed by swarms of the net-spinning caddisfly, Smicridea fasciatella McLachlan. Nuisance caddisflies pose several public health concerns, including asthma, dermatitis, and mental anguish, and the presence of large swarms can negatively impact waterfront recreation and tourism. Here, survey responses from 123 riverfront homes in Bullhead City, Arizona, were used to assess the nuisance status of S. fasciatella and the perceived effectiveness of area-wide abatement strategies. In 2021, 68% of surveys indicated that nuisance caddisfly conditions were uniformly "intolerable" with no significant differences by location, length of residency, or participating recreational activities. Residents identified that S. fasciatella started to become a nuisance between 2015 and 2016, starting in May and ending in November each year. Proximity to swarming adults, disruption of leisure activities, and maintenance associated with sweeping expired caddisflies were among the biggest complaints. Notably, 58% selected "staying inside" as the most effective strategy to avoid direct contact with swarms, and 14% reported asthma-like symptoms from encountering large swarms or sweeping dead, dried adult caddisflies. Riverfront residents supported trout stocking and river flow manipulation as effective measures to reduce S. fasciatella populations. After three years of river flow manipulations, riverfront residents were asked again to describe nuisance caddisfly conditions, and 61% selected "tolerable", signaling improved conditions in 2024. Collectively, these data provide insights into the nuisance status and potential public health risks of S. fasciatella and support continued research of sustainable management efforts to further suppress populations to a tolerable threshold.