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57 annulus ventralis of a Northern crayfish female. In my Nebraska specimens, I have found different females from the same location that have an annulus ventralis which are mirror images of each other. This phenomenon was also mentioned as being seen in Minnesota. 97 HABITATS The Northern crayfish is generally considered to be a non-burrower but occasionally will dig a short and simple burrow. Burrows in clayey streams were shorter than those in loose soil while young crayfish often dug burrows in sandy areas. 96 Streambank burrows are apparently excavated underwater and then extended with openings just above the waterline. At times of low flow, they will excavate a cavity beneath a rock or log to wait for the water to come back. 102 In aquaria studies burrowing could be induced by lowering the water levels. In undisturbed aquaria, they dug a simple burrow under rocks. 91 Another study attempted to induce burrowing in a controlled laboratory setting. Of 36 trials, one crayfish actually constructed a burrow and only five even attempted to burrow. The other 30 "wedged themselves into the drying substatum". 15 Burrowing enables crayfish to survive the freezing of winter and desiccation in summer. The Northern crayfish's intolerance of low dissolved oxygen and their non-burrowing nature will exclude them from the intermittent portions of watersheds. 15 The Northern crayfish cannot withstand any degree of freezing and their non-burrowing puts them at risk with high mortality of immature animals. Their survival mechanism in these areas is to migrate to deeper water or areas that do not freeze rather than burrow. 4 The Northern crayfish is ubiquitous throughout Nebraska and inhabits reservoirs, lakes, ponds, rivers, streams, brooks, and backwaters. In flowing streams it can be found in association with the Calico Crayfish, the Ringed Crayfish and/or the Devil Crayfish. In lakes or reservoirs it is usually the dominant (and only) species. It is almost always associated with some form of cover which can be rock, rock rubble, cobbles, logs or log jams as well as aquatic vegetation. Burrows in stream banks in Nebraska are fairly common in streams with good populations. If these are Northern crayfish "burrows" it is possible that they use these for overwintering as the species virtually disappears from streams when temperatures drop in the fall. Irrigation canals sustain large populations of Northern crayfish and these canals are usually drained in the fall and mortalities are high. Some manage to crawl under riprap and dig holes to survive the winter. BEHAVIOR The Northern crayfish apparently does not maintain a "home" but can roam over a home-range that can be up to 300 meters across. These crayfishes were highly individualistic in their behavior and this complexity makes it difficult to make any generalizations. But, during the day, individuals remained in burrows or under