142 PRACTICAL ZOOLOGY 



Relations of Crustacea to Man. The most obvious relation 

 between the Crustacea and man exists in the case of those species 

 that are used for food. A great many different species are util- 

 ized in this way in various parts of the world ; those most impor- 

 tant in this country are crayfishes, lobsters, shrimps, and edible 

 crabs. 



The crayfishes are not used extensively as food although the 

 difficulty of obtaining lobsters has attracted attention to these 

 smaller relatives, and it is probable that the raising of cray- 

 fishes for market will soon become a nourishing industry. 



Lobsters have long been used as food. They are especially 

 abundant along the coast of Maine, but occur in lesser numbers 

 at other points on our northeastern coast. Lbsters have been 

 captured so persistently, however, that a great decrease in size 

 has taken place, so that where formerly individuals weighing 

 twenty-five pounds were not rare, now they seldom weigh over 

 two pounds. Many efforts have been made to control the catch- 

 ing of lobsters so as to conserve the supply, but thus far with 

 little success. 



The blue or edible crab (Fig. 77, A) comes next to the lobster 

 as an important article of food for man. It occurs along the 

 Atlantic and Gulf coasts, where, just after shedding its exoskele- 

 ton, it is known as the soft-shelled crab. In this condition it is 

 considered more valuable than when the shell is hard. 



The shrimps (Fig. 79) and prawns are smaller than the lobster 

 and crab, and hence of less importance as a food supply for man, 

 though they are captured and eaten in great numbers. 



Value as Food for Fish. -- Although the Crustacea used as 

 food by man in the United States are valued at several millions 

 of dollars annually, still their indirect value as food for fish is 

 probably greater. The smaller Crustacea furnish perhaps the 

 principal item in the fish bill of fare. They are extremely 

 abundant everywhere; at one time there may be more than 

 250,000 in a single cubic yard of lake water and an equal number 

 in an equal amount of sea water. Their effect upon the abun- 



