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14 they had excavated a cavity large enough to fit into but is not really a burrow. BEHAVIOR A long list of other species will eat a crayfish. As a defense, most crayfishes are nocturnal and secret themselves in refugia during the day to avoid predation, especially when molting. Female crayfish with eggs or young use refuges to seclude themselves. In areas where refuges are in short supply, the species that is more successful at retaining possession of a good refuge will be more likely to survive. Crayfish have five levels of reaction to a threat from another crayfish which are: no contest, threat posture, restrained physical contact, claw lock, and strike and rip. 95 "No contest" means one or both will retreat and go about their business. With the "threat posture" they assume a "claws-up" position (see photo at right). At the next level, "restrained physical contact" at least one of them touches the other. With the "claw lock", at least one of them grabbed the other with its claw. Finally, with "strike and rip" they actively went after each other. 43 These reactions can also be seen in fish/crayfish interactions. Crayfish have three responses when approached by a fish including the claws up position, a tailflip retreat and/or no response. Crayfish do not distinguish between a potential predator (rock bass or yellow perch) or a non- predator (darter) as, to them, a fish was a fish and a potential predator. But it was also interesting to note that the crayfish were aware of their relative size. Large crayfishes are less likely to be eaten and usually responded with a claws-up spread. Small crayfishes were more likely to retreat. 131 REPRODUCTION As you may have noted in the Anatomy section, the female crayfish is distinguished by the presence of a structure called the annulus ventralis (seminal receptacle) located between the fifth pair of legs. In the male, the first and second pair of pleopods are enlarged and fold up between the legs. The first pleopod is modified to transfer sperm into the female's seminal receptacle Mature Form I pleopod Immature Form II pleopod Crayfish in "Claws up" posture