APHIDIDiE. True Plant-lice. 
Synonyms. — Aphides , Linn. Aphidina , Burra. Aphidince , Rondani. 
Aphidce , Leach. Aphididce , Passerini. 
This family embraces all of the true plant-lice, of which cabbage 
lice, wheat-lice, the woolly aphis of the apple-tree and the phylloxera 
of the grape-vine, are representatives. It includes some of the most 
destructive species belonging to the entire order, and presents one of 
the strangest physiological facts appertaining to the entire insect class. 
But I must here warn the reader against the very common error of 
supposing that the little black flea-like insects often found on young 
cabbages, turnips and other succulent vegetables are plant-lice, as these 
belong to an entirely different order. The only insects known as 
plant-lice, which are in the habit of leaping, are those included in the 
family JPsyllidcB which have already been described; the true plant- 
ice do not leap, but are usually found stationary in groups or colonies, 
are soft-bodied, and are furnished as heretofore stated, with a slender 
beak with which they suck the juices of the plants on which they are 
found. 
The family contains a large number of species which has caused 
entomologists to search carefully for permanent characters by which to 
divide it into groups or divisions. 
Their small size and the difficulty of preserving specimens for exam¬ 
ination has rendered this aggregation into groups and genera a slow 
and difficult process; and even at the present day it may be truly said 
that no entirely satisfactory arrangement has been reached; that given 
here is based upon what is found in the most recent works on the 
Aphides and my own observations, Buckton, Passerini and Koch being 
my principal guides. 
Before alluding to the classification or arrangement and characters of 
the sub-divisions of the family, or describing species, it is proper I 
should explain the various terms used, with which the unscientific rea¬ 
der is presumed to be unacquainted and give briefly the characteristics 
of the family. 
NOMENCLATURE. 
As an explanation of the more general terms used in Entomological 
writings has been given in previous reports of the State Entomologist 
of Illinois, it is unnecessary for me to repeat it here. I shall therefore 
confine my explanations to the terms relating chiefly to plant-lice, or 
which .are used in a different sense when applied to them, from what 
they are when applied to other insects. 
Larva .—As these insects do not undergo that remarkable transfor¬ 
mation seen in the life of the beetle in its change from a grub (larva) 
to the apparently lifeless chrysalis (pupa) and then to the perfect in¬ 
sect, and in the butterfly in its change from the caterpillar to the 
chrysalis (pupa) and then to the perfect insect with its gaudy colors, 
the term larva does not have the marked signification it does when 
applied to other orders of insects. It may be defined in a general 
sense, as the young, wingless plant-louse. It is similar in form and 
