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33 their whole body. Then they switch to carrying soil. Here they use their claws to grab a clump of moist dirt which they raise towards the body and transfer to the third maxillipeds. The clump of dirt is carried to the top of the burrow where it is arranged around the opening of the burrow which forms a chimney. The larger the chimney, the deeper the burrow. The burrow is dug until it reaches water but if the water level drops, the burrow is deepened. Once the main burrow is dug, extra, extra oblique entrances may be added. Sometimes a burrow is abandoned half-way and a new one started a short distance away. 83 Burrow depths are determined by either the depth to groundwater or the depth at which the ground freezes in winter. This can be as shallow as six inches 227 or more than 12 feet. 17 In Iowa, it was noted that burrows commonly extended straight down for 75 to 100 cm and terminated in a chamber ranging from 8 to 12 cm across. Burrows in small colonies (<10 burrows) or singles were of the single shaft style with only one crayfish per burrow. Occasionally, multi-shaft burrows are found but these still only had one occupant. Occasionally, large colonies may have burrows interconnected and these may be occupied by more than one crayfish. 189 Devil crawfish are seldom able to build a burrow in coarse-grained substrates like sand. Most of the time they could complete a burrow in fine-grained clayey substrates. Mixed substrates lead to intermediate levels of success. Their preference for clayey soils may be that these soils are easier for them to work with. 84 Crayfish burrows have a limited exchange of oxygen with the atmosphere. Oxygen levels measured in burrow water was found to average 1.2 mg/l. This was almost the same as the groundwater at the same site (1.3 mg/l) and much lower than that in the adjacent river (8.4 mg/l). 82 How do they survive such low oxygen levels? Burrowing crayfishes like the Devil crawfish have blood with a high oxygen affinity which enables them to extract oxygen from the low-oxygen burrow habitat. In addition, they spend much of their time in the humid air of the burrow rather than in the water. 157 In Nebraska, they used clay, sandy loam, black loam, gravel, and shaly substrates along clear streams. Near Valentine, their burrows were in the sides of steep banks in sandy loam. The openings were up to three feet above the water and there were no chimneys. 54 I have observed burrows with chimneys like those shown above in eastern Nebraska where heavy clay soils are common. In north-central Nebraska, soils are sandy and I have not seen any burrows with chimneys. Instead I have found simple holes in the stream banks which I have assumed to be crayfish burrows. The photo below shows a pasture in Pawnee County, Nebraska, where burrows were common. The site is on private land a mile west of Burchard Lake and there are no streams flowing