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43 FEEDING AND SPECIES INTERACTIONS One study made direct observations on feeding in ponds. The most common activity was the scraping of algae off rocks. Calico crayfish would also eat the leaves of plants hanging in the water. Aquatic plants were often eaten, (especially by the young crayfish) as was artificial fish feed. One instance of cannibalism was observed (one crayfish eating one recently molted) and one instance of a crayfish eating a fish. 226 Attempting to analyze stomach contents is difficult because crayfish macerate their food into mush. Plant material is often the dominant food item found. Other foods can include zooplankton (Daphnia), insect remains, isopods (Asellus), and midge larvae (Chironomus). Rotifers and diatoms were commonly seen as they were frequently still attached to plant fragments. 226 Perhaps they were eating the plants to get the rotifers? Calico crayfish juveniles were found to filter feed whereas adults may do so opportunistically. 16 Calico crayfish have been tested as a means to control submerged aquatic vegetation. They did so by a combination of eating vegetation and clipping it off. But it would take at least 88 crayfish per square meter to provide adequate vegetation control. 137 Calico crayfish fed on submersed macrophytes in the Lake of the Woods but did litt6le damage. 121 DISTRIBUTION The range of the Calico crayfish extends from the Continental Divide in Colorado, Wyoming and Montana eastward to Maine and from Kentucky to Canada. It has been introduced into Europe (Germany) and Canada. 114, 121 The species is widespread in Nebraska, typically (though not exclusively) found in slower, silt-bed streams. It has not been found in the Little Blue basin, there is only one record for the Republican basin and it is uncommon in the Big Blue basin. In the White River/Hat Creek basin, it is the dominant species. Its distribution in the upper Niobrara River is interesting. From the Wyoming state line to Agate Fossil Beds National Monument, the Ringed crayfish is the dominant species. At Agate, Ringed crayfish and Calico crayfish can be found together. Between Agate and Box Butte Reservoir, the habitat changes with aquatic vegetation declining markedly and only Calico crayfish are found. Within Box Butte Reservoir we find only Northern crayfish but below Box Butte Reservoir, Northern crayfish and Calico crayfish will both be found for a short distance after which the Calico dominates for several miles. IMPACTS The Calico crayfish has been introduced into Europe and into several Canadian lakes. 114, 121