VALUE OF BIRDS TO MAN. 29 



The rapidity of propagation shown by some insects is per- 

 haps without a parallel in the animal world. 



In order to give some idea of the powers of multiplication 

 of the Colorado potato beetle, the Canadian 

 Entomologist states that all its transformations 

 are effected in fifty days ; so that the result of 

 a single pair, if allowed to increase Avithout 

 molestation, would in one season amount to 

 over sixty millions. 1 beetle - 



Speaking of the great power of multiplication shown by 

 plant lice or aphids, Dr. Lintner says that Professor Rilev, 

 in his studies of the hop vine aphis (PJiorodon humuti), 

 has observed thirteen generations of the species in the 

 year. Xow, if we assume the average number of young 

 produced by each female to be one hundred, and that every 

 individual attains maturity and produces its full complement 

 of young (which, however, never occurs in nature), the 

 number of the twelfth brood alone (not counting those of 

 all of the preceding broods of the same year) would be 

 10,000,000,000,000,000,000,000 (ten sextillions) of indi- 

 viduals. Where, as in this instance, figures fail to convey 

 any adequate conception of numbers, let us take space and 

 the velocity of light as measures. Were this brood mar- 

 shalled in line with ten individuals to a linear inch touching 

 one another, the procession would extend to the sun (a space 

 which light traverses in eight minutes) , and beyond it to the 

 nearest fixed star (traversed by light only in six years), and 

 still onward in space beyond the most distant star that the 

 strongest telescope may bring to our view, to a point so 

 inconceivably remote that light could only reach us from it 

 in twenty-five hundred years. 



The remotest approach to such unchecked multiplication 

 on the part of this insect might paralyze the hop-growing 

 industry in one season. While the aphids may represent 

 the extreme of fecundity, there are thousands of insect 

 species the unchecked increase of any one of which would 

 soon overrun a continent. Mr. A. H. Kirkland has com- 



1 Report of Townend Glover, entomologist, in Annual Report of the United 

 States Commissioner of Agriculture, 1871, p. 74. 



