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 id 
are effected in fifty days; so that the result of AD 
a single pair, if allowed to increase without wy" 
molestation, would in one season amount to eae ae 
over sixty millions.! beetle: 
Speaking of the great power of multiplication shown by 
plant lice or aphids, Dr. Lintner says that Professor Riley, 
in his studies of the hop vine aphis (Phorodon humuli), 
has observed thirteen generations of the species in the 
year. Now, 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. 
