CRAYFISHES OF NEBRASKA AND EASTERN COLORADO 
95 
IN COLORADO 
The State of Colorado is drained by three major river systems — the Rio Grande, 
the Colorado, and the Mississippi. The area covered by this study is that which 
lies east of the Continental Divide and is in the drainage system of the Mississippi 
River. 
Arkansas River. — A collection of C. virilis from St. Charles River, a tributary, 
near Pueblo. 
Smoky Hill River. — A collection of C. simulans near Oriska, Kit Carson County. 
Arikaree River.— -A collection of C. neglectus from Yuma County and another 
collection of C. neglectus from Black Wolf Creek, a tributary of the Arikaree 
River. 
South Platte River. — At Julesburg, several collections of C. neglectus and C. 
virilis. At the Empire Reservoir, Weld County, draining from the Platte River, 
collections of C. immunis, G. immunis spinirostris, and G. diogenes. From the 
Poudre River, Larimer County, G. diogenes and G. immunis. From Middle Boulder 
Creek and South Boulder Creek, G. diogenes and G. virilis, and from adjacent ponds 
G. immunis. From creeks and ponds in Douglas County and in Denver County, 
G. immunis and C. virilis. 
ECOLOGY AND LIFE HISTORIES 
The ecology of crayfishes has been studied by Harris (1900, 1901, and 1903), 
who summarizes the work done by previous workers. Ortmann (1906) has studied 
the ecology of eastern species, but aside from the work of Harris no one has con- 
sidered the special habitats of crayfishes in the Missouri River drainage. Some 
attention was therefore given to the ecological factors of crayfish distribution in 
Nebraska. 
Six species of the genus Cambarus are found in Nebraska, three of which have 
a wide distribution; the remaining three have been found only in restricted areas. 
Cambarus immunis has the widest distribution within the State, and the 
writer has given considerable attention to its habitats. This species was previously 
studied by Harris (1901) in Kansas. This is the mud crayfish. In Nebraska it is 
the only form that persistently inhabits the small ponds, many of which contain 
water only during the spring and early summer. The life of this species in periods 
of drought and their migration to other ponds is not known. I have found speci- 
mens in a dry pond near Lincoln in May, living in a small amount of water at a 
depth of 32 inches. The pond received only small amounts of water from local 
rains through the summer. 
This species usually digs a straight burrow with a small, shapeless chimney in 
heavy black soil, rich in decaying vegetable material (fig. 2). Many individuals 
are found in temporary ponds early in the summer in small burrows several inches 
in depth, under small stones (fig. 3), empty cans, or decaying logs. According to 
W. P. Hay (see Evermann and Clark, 1920, pp. 83-86) this is a characteristic also 
of C. propinquus from Indiana. 
This is the only species I have observed in the act of chimney building. The 
process is carried out on cloudy days or, as in the cases observed in this study, in 
