generation the ninety children would produce 8,100 young; in 
the third generation there would be 729,000 ; in the fourth 
65,610,000; and in the fifth generation there would be from 
the preceding 5,904,900,000, which would yield a progeny of 
531,441,000,000. Now you can understand whence the millions 
of plant lice come, when, in early spring, you find the young 
growth of plants literally covered with these minute insects. 
You can understand, too, how plants must suffer when their 
vital fluids are being extracted by the thousands of these little 
insects. 
This fact in the life history of animals is expressed by the word "vivip¬ 
arous”, meaning bearing alive, as opposed to "oviparous”, or the bearing 
of eggs. And these females are called agamic females, because the young 
are produced without the marriage of sexes. 
This rapid multiplication of individuals is greatly operated 
against by diseases and enemies, and even by unfavorable 
weather. Therefore, we are not in danger of being driven 
from the face of the earth by increasing multitudes of these 
minute insects. 
The insect enemies of plant lice are of two classes, those 
which eat the lice or suck their juices and those which lay 
their eggs within the bodies of the lice for the larvae to de¬ 
velop there. The first class is termed predaceous insects , and 
familiar examples are the ladybird beetles, the little shining, 
hemispherical beetles, highly colored, red or yellow, with two or 
more black spots. The larvae, as well as the beetles, devour the 
plant lice. The second class is termed parasitic insects , and the 
most common instance is that of a little ichneumon fly (Aphid - 
ius), not much larger than a full-grown aphis. It looks like a 
minute honey bee, and belongs to the same family. It pierces 
the aphis and inserts an egg. The larva from this egg lives in 
the body of the plant louse and causes it to swell and die. You 
may find clinging to plants the dead pearly bodies of such lice, 
with a circular piece of the back neatly cut out, hanging by a 
bit of the edge. From such a case the aphidius has escaped. 
I have had five full-grown wingless females in captivity, and 
in two days they were attended by thirty-eight young ones, 
showing an average of four young per day to each insect. 
The life of an individual is eight days to maturity and about 
5 
