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The life cycles of Dina dubia and Erpobdella punctata were described from semimonthly (monthly in winter) collections made at two sites on Canagagigue Creek between May 1982 and July 1983. Observations on reproduction were made in the creek and in a flow-through stream tank. Most individuals of both species completed their life cycles in about 1 year, but some required 2 or more years to reach sexual maturity. The estimated average fecundity (138–173 young/adult), growth rate, and maximum size (1946 mg live weight) of E. punctata were all greater than for D. dubia (47–50 young/adult; maximum size, 725 mg), but D. dubia was much more abundant in Canagagigue Creek. Both species fed most frequently on Chironomidae and Oligochaeta, with the total variety of prey consumed reflecting the diversity of prey available at the site. The habitat preferences of the leeches were apparent from their diets: D. dubia ate relatively more animals associated with riffle habitats; E. punctata ate relatively more pool-dwelling organisms. The greater abundance of D. dubia at our study sites is attributed to this difference in habitat preference.

Fifth-instar larvae of the caddisfly Neophylax fuscus Banks (Trichoptera: Limnephilidae) enter a 4-month diapause in April after aggregating on the undersides of stream rocks in gravel cases. Aggregations have up to several hundred members, and densities within aggregations range from 1000 to 17 263 cases/m2. Field experiments conducted between 1984 and 1986 showed that larvae preferred to settle where initial larvae had already attached, but that there was no evidence for a chemical cue for aggregation. Mortality during the diapause but before pupation averaged 37.9%. Both exposure to low water and high density within aggregations contributed to increased mortality. Parasitism and predation appeared to be rare. The developmental synchrony of pupae and emergence synchrony were related to aggregation density during diapause. Low density aggregations tended to have low synchrony of development and emergence, while high density aggregations had higher synchrony.