Predation on the erpobdellid leech <i>Nephelopsis obscura</i> in the laboratory

Six size classes of Nephelopsis obscura ranging from cocoons through hatchlings (2–4 mg) to mature individuals (150 mg) were exposed to a range of potential predators and also tested for cannibalism. Neither cannibalism nor interspecific leech predation was found, but nine species of Coleoptera, Amphipoda, Hemiptera, and Zygoptera consumed one or more size classes of N. obscura. In general, predation rates were highest on individuals &lt;10 mg and declined with increasing size of N. obscura. Larger predators (intra- and inter-specifically) usually had higher consumption rates than smaller ones. Because of the high abundance of the nine species of predators in prairie pothole lakes during the summer, it is speculated that predation on N. obscura hatchlings and cocoons is directly related to the recorded reductions in these size classes in the macrophyte zones during the summer.