6 
Some of the grandest problems that relate to animal life, belong 
to the study of these little animated grains, and if ever solved, will, 
in all probability, be solved by carefully studying their life history. 
As they stand, to a great extent, isolated, even in the order of 
insects to which they belong, it is necessary, in order to understand 
the characters by which they are classified, and described, to adopt a 
somewhat peculiar system of nomenclature for the group. In order 
therefore to render this synopsis as complete as possible within the 
limits to which it is restricted, it is necessary to give at least a brief 
account of this system and an explanation of the terms used which 
are peculiarly applicable here, or which are used in a different sense 
from that in which they are generally applied in entomology. 
In an economic point of view, their importance is undoubtedly 
greater than generally supposed. Their small size causes them to be 
overlooked to a far greater extent than those who are acquainted 
with them are willing to believe. I have been astonished since I 
commenced to study them carefully, to find very many old and ^ ex¬ 
perienced agriculturists who are wholly unacquainted with them by their 
jj; common name, Plant-Lice. 
Their quiet and silent method of operating, drawing so gradually 
upon the vitality of the plant, is another reason why attention is not 
l more frequently drawn to them. It is, therefore, only, when they de¬ 
velop in immense numbers on some important cultivated plant, as 
1 wheat, hops, etc., that any particular notice is paid to them. 
The appearance of'the grain plant louse, ( Siphohiopn.org granana,) 
last summer, upon the wheat in the southern part of the state, ex¬ 
cited universal alarm— few farmers being able to determine the 
character of the insect—some supposing it to be the chinch-bug and 
others the Hessian-fly, although aware from an inspection of them that 
they differed in some respects from either of these species. 
These facts, together with the fact of their capability of increase with 
a rapidity, perhaps unequaled in .the entire insect class, render them 
of sufficient importance to receive the notice here given, in a work 
on economic entomology. It is proper to state here that the terms 
Aphididae and Plant-lice, in the title of this work, are used in the 
broad sense, including the leaping plant-lice as well as the true 
aphides; further on, when the distinction is shown, these terms will 
be restricted to their proper groups. 
On account of their general similarity in appearance and habits, or- 
I; dinary observers have been content with simply designating them by 
their common name. They somewhat closely resemble each other in 
general appearance, as well as in the habit of subsisting upon the 
juices of the plants on which they reside, it is true ; but when we 
come to examine them closely and compare them carefullv one with 
! another, we find there are marked differences in the details of their 
| external anatomy as well as their habits, showing not only that there 
is a vast number of different species, but also that the species iread- 
ily admit of being aggregated or arranged into groups by common 
characters; or, in other words, that there are generic and family 
differences, as well as specific differences among them. 
