248 XEW YORK STATE MUSEUM 



defenseless insects, were it not for the fact that they were exceecHngly pro- 

 lific. This subject early attracted the attention of naturalists, and we have 

 the record of ReaTimer's experiments which show^ that a single plant louse 

 might in one year of uninterrupted breeding under favorable conditions 

 become the progenitor of the enormous number of 5,904,900,000 individuals. 

 This immense number is beyond the ready grasp of most persons and we 

 may perhaps appreciate it a little more by the following calculation. The 

 average length of most plant lice would be approximately '8 inch, but if we 

 call it ' ,„. which is certainly a very moderate estimate, and group this host 

 of individuals in a column of four, which is the ordinary military formation, 

 and bring each tile closely behind the other, we w^ill have an army long 

 enough to encircle the globe at the equator and enough would remain to 

 stretch across this continent, or in other words we would have an army 

 27,952 miles in length, all possible descendants from a single plant louse in 

 one season. This almost passes credibility, yet the same thing has been 

 figured out by another competent naturalist, namely Huxley, who estimated 

 that from the uninterrupted breeding of 10 generations from one individual, 

 there would result a mass of organic matter equal to the bulk of 500,000,000 

 human beings, or about the population of the Chinese Empire. The enor- 

 mous number of these insects occurring on a tree is shown by the calculation 

 of Dr Fitch, who estimated that on one small cherrytree there were over 

 12,000,000 aphids. Such facts as these illustrate the possibilities and show 

 in no uncertain manner the immense value of the natural checks enumerated 

 above. 



Short life cycle essential to prolificacy in plant lice. This startling pro- 

 lificacy is not brought about by the production ,of immense numbers by any 

 individual, but, as is the case with, many other animal.s, is accomplished by 

 the extraordinary rapidity with which the life cycle is completed. This is 

 admirai)h- illustrated by the hop aphis, Phorodon humuli .Schrank. 

 The cold season is passed in what is known as the winter egg and the young 

 insect hatching therefrom, known as the stein mother, begins to produce 

 •young when two or three days old, bringing forth from two to seven daily, 

 and each of these in turn begins to produce \-oung in about eight days. It 



