248 NEW YORK STATE Ml"SEUM 



defenseless insects, were it not for the fact tliat they were exceedingly pro- 

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

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

 might in one year of uninterrupted breeding vmder favorable conditions 

 become the progenitor of the enormous numljcr of 5,904,900,000 indi\i(luals. 

 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 |)l;uit lice would be approximately 's inch. l)ut 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 file closely behind the other, we will have an army long 

 enough to encircle the globe at the e(}uator 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 descentlants from a single ])lant louse in 

 one seas(jn. This almost passes credibility, yet the same thing has been 

 figured out b\ another competent naturalist, namely Huxley, who estimated 

 tliat from the uiiiiu< rru])tc(l Ijrccding of 10 generations from one iiiili\idLial, 

 there would result a massot organic matter ecpial to the bulk of 500,000,000 

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

 mous number of tlu;se insects occurring on a tree is shown b\- the calculation 

 of l)r Fitch, who estimated that on one small cherrytree there ^vere 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. Tliis startling pro- 

 lificacy is not ijrought about by tlu: i)roducti<>n of immense numljers b\' any 

 individual, but, as is the case with many other animals, is accomplished by 

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

 admirably ilkislralrd Uy the hoj) 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 stem mother, begins to produce 

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

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



