136 PRACTICAL ZOOLOGY 



The injuries done by crayfishes take place in rather restricted 

 localities. Earthen dams, dikes, and fills are sometimes harmed 

 by their burrows, and in the Houston clay lands of Mississippi 

 and Alabama certain areas are so badly infested by burrowing 

 crayfishes that the raising of crops with profit is impossible. 

 The area damaged by these crayfishes is about one thousand 

 square miles. In some places there are over ten thousand of 

 their holes per acre. Cotton and corn plants are cut away by 

 the animals and taken into their burrows to be used as food 

 (Fig. 76) . 



The most practical and economical means of coping with the 

 crayfish problem is to combine poisoning with killing the crus- 

 taceans by mechanical mean's. During rainy weather and at 

 twilight in the spring after the crayfish become active, the area 

 to be planted with cotton or corn should be visited frequently, 

 and as many as possible of the crayfish killed before seeding time. 

 After the majority have been secured the remaining occupied 

 burrows should be treated with poison, preferably carbon bi- 

 sulphide (Fisher). 



REFERENCES 



The Crayfish, by Thomas Huxley. 



Introduction to Zoology, by R. W. Hegner. The Macmillan Co., N. Y. 

 City. 



The American Lobster, by F. H. Herrick. Bulletin U. S. Fish Commis- 

 sion, Vol. XV. 



