Life Cycle and Reproduction of Nephelopsis obscura Verrill (Hirudinea:Erpobdellidae) in Permanent Ponds of Northwestern Minnestoa

Abstract

The bait leech, Nephelopsis obscura, followed a 24-month life cycle in two natural ponds of northwestern Minnesota, Priem's Pond and Early's Pond. Clitellum development required an approximate minimum weight of 1.20 g and mature leeches died shortly after depositing cocoons on aquatic vegetation at midsummer. The onset of maturity was correlated to rising water temperature (r=0.98) and lengthening photoperiod (r=0.93). Seasonal depth movement of leeches was obseved in Priem's Pond and was attributed to oxygen depletion at lower depths during midsummer stagnation.