Abstract
Over 18,000 caddisfly specimens representing 44 species were collected from sunset until sunrise on each of 6 days during July 2010 from a large river in northern Lower Michigan. Sampling occurred every 15 minutes from sunset until midnight and every hour afterward until sunrise. Mean specimen abundance peaked at 22:30, approximately 1 hour after sunset, before decreasing precipitously. Species richness peaked from 22:30 to 23:00 and decreased more gradually. All species and >95% of specimens were caught before midnight. Both overall specimen abundance and species richness correlated positively with dew point, reflecting relatively constant temperatures throughout the sampling period. Likewise, temperature correlated positively with specimen abundance at each sampling period from 23:00 to 00:00 and at 02:00. Of the 18 most abundant species, 10 had peak abundance between 22:30 and 22:45, 7 had extended peak abundance from 22:30 to 23:00 to 02:00, and 1 peaked after 22:30. Specimen abundance of all trophic functional groups peaked from 22:30 to 22:45, except for scrapers, which remained abundant until 23:30. Our results suggest that 1–2 hours after sunset is the optimal time for sampling adult caddisflies, but sampling until 2–3 hours after sunset is necessary to collect all species. Stopping a sample when specimen abundance starts to decrease may miss peak species richness. Ambient temperature must also be taken into consideration.