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86 However, aquatic vegetation is a poor food for crayfish as it is low in nutrients. 164 It may be that Rusty crayfish are clipping off the plants to look for macroinvertebrates on those plants or just to get the plants out of their way. This is supported by the observation that they take no further interest in the plants after they cut them off. 143 They may eat some because there is nothing else to eat or as incidental ingestion while eating the attached organisms. 165 . Aside from aquatic plants, foods eaten include snails. 141, 143, 186, 251 , freshwater mussels and fingernail clams 132 , aquatic insects 251 , other aquatic crustaceans 251 and fish eggs. 129 Information on the ability of Rusty crayfish to consume Zebra mussels (Dreissena polymorpha) is mixed. In one study, they were tested in cages and there was a 31% reduction in Zebra mussel density. 186 However, a similar study contradicted this finding where they found little or no reduction. It is possible that the lack of alternative foods in the former study may have forced the crayfish to eat the Zebra mussels. 223 PRODUCTION AND GROWTH Aging crayfish is almost impossible but it is estimated that, on average, they live 2 ½ years. 191 In Illinois, the largest male collected was 40.5 mm CL while the largest female was 41.5 mm CL. 180 IMPACTS The Rusty crayfish has been widely introduced outside of its native range. There have been many impacts noted, mostly negative. Nonnative Rusty crayfish have been displacing or had other impacts on native crayfishes in many areas. 22, 144, 174 The Rusty crayfish was introduced into Wisconsin waters in 1965. Prior to that, the native Northern crayfish was present in 62% of collections whereas, since 1985, they have dropped to 34%. 173 When tested together, the Northern crayfish had poorer growth and higher predation by Largemouth bass than Rusty crayfish. 73, 99 All crayfishes use shelter to avoid predators and, where shelter is in short supply, the Rusty crayfish is better at displacing other crayfishes. The result is that the other crayfishes are forced to use poor shelter which leads to higher predation. 73, 132 The Spinycheek crayfish is native to the eastern seaboard from Maine to Virginia. Within this range, it is rapidly disappearing due to competition with introduced Rusty and Northern crayfish. 139