PHYLUM ARTHROPODA — CLASS CRUSTACEA 267 



Habitat and Behavior 



For the most part crayfishes (crawfishes, crawclads, fresh-water 

 lobsters) are inhabitants of fresh-water streams and ponds where 

 there is sufficient calcium carbonate in solution for purposes of 

 skeleton formation. These animals may be found moving about on 

 the bottom, or they may be in hiding under some stone or log, or 

 they may be in the mouth of a burrow beneath the water's edge. 

 Some species carry air tunnels vertically from the original hori- 

 zontal burrow to the surface of the earth and deposit mud around 

 the opening of a tunnel. They are much more active at night than 

 during the day. It is possible for them to walk about on the bottom of 

 the stream or pond, moving the body in almost any direction. Their 



Fig. 152.— Cavibarus clarkii, the swamp crayfish, a very common species in the 

 swamps ol: the Southern States. (Courtesy of Southern Biological Supply Co.) 



swimming habits are rather peculiar in that they dart backward 

 through the water, as a result of the strong downward stroke of 

 the tail. One stroke of the tail will carry the animal a yard and 

 this is commonly sufficient to avoid the enemy. The daytime is 

 usually spent in hiding under objects or in the mouth of the bur- 

 row. Crayfishes may at times desert their aquatic habitat and go 

 foraging out over swampy land. In some localities certain species 

 build their burrows down to the subterranean water table right 

 out in the fields and become important pests. Sight, touch, and 

 chemoreception are important senses in this animal. 



The crayfish captures other animals, such as tadpoles, small 

 fish, and aquatic insects, by waiting in hiding and suddenly seizing 



