20 MAN AND ANIMALS 



IV. THE ECONOMIC IMPORTANCE OF ANIMALS 



Why study bugs ? Why waste your time upon that which can bring 

 in no money? Why study insects, worms, birds, or snakes? These 

 are questions which are often asked of the zoologist, especially such as 

 go into the field to study and collect animals and accordingly meet the 

 public. They are questions which the zoologist seldom can answer to 

 the satisfaction of the inquirer, who not infrequently thinks the observer, 

 if alone, is somewhat insane. Indeed, the conduct of one Chicago 

 entomologist led to a police inquiry into his sanity. His offense was that 

 of collecting insects under an electric light. The questions above we 

 shall not attempt to answer here, except by asking, "Why study any- 

 thing?" 



We have already noted the complexity of the problems of our relation 

 to nature. We have noted the disturbed balance, the ravages of species 

 introduced by accident and by official act. We have noted that knowl- 

 edge is necessary as a basis for "sanity toward nature." We have still 

 to call attention to some of the economic values of animals. 



It follows from the nature of the animal community and the close 

 interdependence of the various species that every species is of some 

 importance in the chain of food, space, and other relations, and every 

 species is therefore of some economic importance. A few are of great 

 economic importance. In addition to this we have certain definite 

 practical uses and well-known matters of importance attached to each of 

 the animal groups. Taking the various groups in their taxonomic order, 

 we note the following: 



The protozoa are one of the important sources of food of larger forms. 

 Also about a half-dozen human diseases are known (27) to be due to them, 

 and the list is continually growing. The shells of extinct species are 

 an important part of chalk. 



The uses of sponges are familiar. Aside from their importance as 

 food of other forms, the coelenterates furnish us with corals' of all sorts. 

 Among the echinoderms the starfish is an important enemy of the oyster 

 and mussel beds (28). The flatworms are important as parasites, many 

 species having been recorded in the body of man (29). The round worms 

 are of considerable importance in the same way, and some are serious 

 enemies of grain. The earthworms are of much value to the soil (30). 

 The crustaceans are the most important aquatic invertebrates, the 

 Entomostraca being, from the standpoint of food supply, to the waters 

 what rooted plants are on the land, one of the things to which nearly all 

 food interaction can be traced. Some are used as food (lobsters, shrimps, 



