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40 As there are no keys for female crayfish, they are identified by their association with, and similarity to, male crayfish collected from the same area. Since we have only five species in Nebraska, the secondary characteristics noted above will generally work. At right is the annulus ventralis of a female Calico crayfish. The upper portion of the photo is towards the crayfish's head. HABITATS Numerous authors have noted that the Calico crayfish is most commonly found in areas with slow or no flow and muddy bottoms. 89, 180, 188, 226 They are tolerant of low oxygen and high turbidity. 15, 226 They are seldom found in streams with coarse bottom substrates and moderate currents. 226 But this may not be an indication of a preference for muddy substrates. Testing Northern crayfish and Calico crayfish separately in a tank with equal amounts of mud, gravel and rock substrates found that both species preferred the rock. 15 In the Lake of the Woods where the Calico crayfish is an introduced species, they preferred areas that with organic and inorganic fines and near beds of vegetation. 121 It has been long known that the Calico crayfish is a burrowing species. But they tend to burrow only when their ponds are drying or when winter approaches. Burrows usually went straight down anywhere from 15 inches to four feet and ended in a large cavity. 19 In a hatchery, burrows in pond banks went in horizontally and also ended in a cavity. Often the burrows were sealed with clay or mud. 226 In the Maple Creek watershed of Nebraska, Calico crayfish burrowed to avoid summer drying and for overwintering. Two burrows were excavated and found "to be in excess of 1 m deep". 210 BEHAVIOR As has been noted for crayfish in general, adult Calico crayfish are mainly nocturnal. Through direct observation in ponds, the number that were visible from any single