MAN AND INSECTS HOWARD 397 



and phosphorus. The starches and other substances that make the 

 skeleton of insects, abound in nature ; while the diet of man must be 

 selected carefully to include the substances needed for the pjrowth of 

 bone. The blood of insects ponetratos to every part of the body, 

 just as it does with us, but the air that purifies the blood also 

 penetrates to every part of the body instead of beinfj confined to the 

 Um»^s. When insects are born, there is no long period of helpless 

 infancy; they take care of themselves from the start. There is no 

 feeble old a.^e with insects; when their work is done they die before 

 their faculties or their structure have bep;un to degenerate. Tiiere 

 are no bones to grow brittle with age; chitin seems to grow stronger 

 with age. 



Together with the advantages already pointed out comes the 

 tremendous advantage of rapidity of multiplication and rapidity 

 of growth and the consequent rapidity of the accommodation of a 

 species to a changed environment. Insects, for example, have all 

 the way from 1 to 20 generations a year, nature trying slowly to 

 make each generation more fit than its predecessor. Place the 

 number at five per annum, as is the case with the cotton boll weevil. 

 Then, in the 35 years this insect has lived in the territory of the 

 United States, it has had 175 generations. An equal number of 

 generations for the human species would fill more than JJ,000 years. 

 The advantage in the slow process of evolution and accommodation 

 to changed conditions is evidently enormous. 



As to rapidity of multiplication (which differs very greatly with 

 the different forms of insect life) two rather striking examples may 

 be cited. I have shown that, with the common house fly, a single 

 overwintering female may have, between April 15 and September 10, 

 5.598,720,000.000 descendants. This seems almost incredible, but, 

 given larval food, it is possible. It is not, however, great as are the 

 figures, as startling as the estimate made by Prof. G. W. Herrick of 

 Cornell, of the ponderable mass of the descendants of a single cab- 

 bage aphis in Central New York in less than a year. Although a 

 single aphis weighs little more than a milligram, the ponderable 

 mass of its descendants in less than a year would be more than 822,- 

 000,000 tons! In pounds, this would be 1,044,000,000,000. Esti- 

 mating the human population of the world at 2,000,000,000 and the 

 average weight at the exaggerated figure of 150 pounds, the total 

 human weight would be 300,000,000,000 pounds. In other words, the 

 plant-lice descended from one individual of one species in a single 

 season would weigh more than five times as mucii as all the people 

 of the world. Of course, in this estimate we must grant the existence 

 of food enougli for this mass, which of course is imi)ossible. 



I have .spent the larger part of my time during the past two years 

 in writing a history of applied entomology, and it is interesting to 



