The introduction of the rusty crayfish, Orconectes rusticus, has large effects on freshwater communities by displacing native crayfish species and altering macroinvertebrate communities. We used laboratory studies of aggression, shelter use, and feeding to examine the relationship between O. rusticus and a crayfish native to the Northeast, Orconectes limosus, along with these species' consumption of native bivalves. Orconectes rusticus dominated O. limosus in aggression trials, and shelter trials showed that dominant crayfish obtained shelter over subordinate crayfish. Both species of crayfish consumed freshwater mussels (Unionidae) and fingernail clams (Sphaeriidae), preferring prey of smaller size and those that were not buried. These findings suggest that the invasion of O. rusticus may pose a threat to native crayfish and the already threatened bivalves of the Northeast.