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 zodlogist, especially such as 
go into the field to study and collect animals and accordingly meet the 
public. They are questions which the zodlogist 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, 
