PROTECTION OF BIRDS—COLLINGE. 851 
examination of a few instances will at once serve to show how true 
it is. 
We are all familiar with the greenflies on the rose and have some 
confused idea of their enormous fecundity. We probably call to 
mind Prof. Huxley’s computation of their amazing rate of increase, 
but few of us have ever seriously considered the potential danger of 
ereenflies with reference to our food supply. 
The late Prof. Riley, when ‘studying the hop aphis, observed 13 
generations of this species in a year. Assuming the average number — 
of young produced by each female to be 100 and that every individual 
attained maturity and produced its full complement of young, “the 
number of the twelfth brood alone (not counting those of all the pre- 
ceding broods of the same year) would be 10,000,000,000,000,000,- 
000,000 (10 sextillions) of individuals.” Such figures fail to convey 
any idea of the numbers, but dealing with these Prof. Forbush has 
pointed out that if these individuals were marshaled in line with 
10 to a linear inch and 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 view, to a point so inconceivably 
remote that light could only reach us from it in twenty-five hundred 
years.” 
But there is scarcely a cultivated plant that is not attacked by one 
or more species of greenfly, or aphid, as the naturalist terms them. 
Of the trillion of billions that infest the apple, pear, plum, and cherry 
trees, and the hops, wheat, beans, turnips, cabbage, etc., what be- 
comes of them? They are eaten by the birds. Aphids in large quan- 
tities have been found in the stomachs of the whitethroat, the war- 
blers, the tits, the wren, the goldfinch, the chaffinch, the skylark, and 
numerous other birds; and the same remarks hold good with refer- 
ence to the insidious scale insects. 
Most insects do the greatest amount of damage during their larval 
or caterpillar stage; they feed voraciously, their daily consumption 
of food often exceeding many times the weight of their bodies. Se- 
lecting a familiar example, the yellow-and-chocolate marked cater- 
pillar of the currant or magpie moth, it requires about 170 of these 
to weigh an ounce; in their earlier stages, say, about 200. We have 
seen currant plantations infested: with these and by counting the 
number on one bush have estimated nearly 1,000,000 to the planta- 
tion, or a total of 24 hundredweight. Had these been left undis- 
turbed they would quickly have consumed the whole of the currant 
leaves and ruined the crop; but, thanks to the birds, they were de- 
duced to insignificant dimensions long ere they had an opportunity 
of devastating the bushes. And so it is with numerous other crops. 
