Predatory effectiveness of two vernal-pool copepods, Acanthocyclops vernalis (Fischer) and Diacyclops bicuspidatus thomasi (Forbes), was assessed against cohabiting larvae of Aedes canadensis (Theobold) and Aedes stimulans (Walker) in laboratory bioassays. D. b. thomasi did not exhibit predatory behavior toward first instars, even when both organisms were confined in 35-mm wells for 7 d and alternative food sources were not available. A. vernalis did feed on early instars, but its effectiveness was significantly influenced by the presence of alternate food, the size of the container, and the size and age of the larval prey. Results strongly suggest that in a comparatively unrestricted natural vernal-pool habitat where an abundance of other food sources are available, neither copepod species plays a major role in reducing larval mosquito populations.