BIOLOGY AND HUMAN WELFARE 405 



2. Insects Injurious to Animals 



The former Chief of the United States Bureau of Entomology 

 informs us that Insects alone in this country continually nullify 

 the labor of a million men, in spite of the annual expenditure of 

 between two and three hundred million dollars in fighting insects, 

 and if human beings are to continue to exist they must first win the 

 war. This can only be accomplished by the labors of an army of 

 patient and skilled investigators, and will occupy very many years, 

 possibly all time to come. This is not only because the insect 

 complex is enormous — there are possibly three million species 

 of which only about six hundred thousand have been described — 

 but also because insects achieved an important place on this globe 

 many millions of years before Man came into existence, and to-day 

 are probably the most perfectly adapted of all creatures to live 

 under all sorts of environmental conditions. If this statement 

 appears extreme, the following examples will serve to make clear 

 some of the cardinal facts which are necessary for an appreciation 

 of the stupendous problems involved. 



Among this teeming insect population, probably the Botflies, 

 Fleas, and Lice stand preeminent as parasites of Man and beast. 

 Botflies of various kinds infest domesticated animals but rarely 

 human beings. The most common Horse Botfly attaches its eggs 

 to the Horse's hair where the eggs can be licked off and swallowed. 

 Then the larvae spend nearly a year attached to the lining of the 

 stomach, and if present in considerable numbers cause irritation 

 and serious digestive disturbances. When full grown the larvae pass 

 out with the feces, pupate in the ground and emerge as adult bot- 

 flies. 



Again, the common Ox Botfly deposits its eggs chiefly on the 

 legs of Cattle, but when the larvae emerge, they penetrate the hide, 

 and then wander through the tissues until the following spring. 

 Finally they come to rest just under the hide of their host, which 

 they puncture to get air. When the larvae are ready to assume the 

 pupal state they burrow out, drop to the ground and there com- 

 plete their life history. It is estimated that the monetary loss from 

 the Ox Botfly alone in the United States is about one hundred 

 million dollars annually. (Fig. 256.) 



Fleas and Lice of various species are common parasites of the 

 higher animals throughout most of the world. The Jigger Flea 



