We report results of a study that made reciprocal comparisons of environmental DNA (eDNA) assays for two major invasive crayfishes between their disparate invasive ranges in North America. Specifically, we tested for range expansions of the signal crayfishﾠPacifastacus leniusculusﾠ(Dana, 1852) into the Laurentian Great Lakes region known to be invaded by the rusty crayfishﾠOrconectes rusticusﾠ(Girard, 1852), as well as for the invasion ofﾠO. rusticusﾠinto large lakes of California and Nevada, US known to be invaded byﾠP. leniusculus.ﾠWe compared eDNA detections to historic localities forﾠO. rusticusﾠwithin the Great Lakes, and to recent sampling for presence/absence and relative abundance ofﾠP. leniusculusﾠin California and Nevada via overnight sets of baited traps. We successfully detectedﾠO. rusticusﾠeDNA at six sites from the Great Lakes andﾠP. leniusculusﾠfrom six of seven lakes where it was known to occur in California and Nevada, but did not detect any range expansions by either species across the North American continent. eDNA appears suitable to detect benthic arthropods from exceptionally large lakes, and will likely be useful in applications for monitoring of new biological invasions into these and other freshwater and marine habitats.