17 0 
Pig 1 42. 
They usually pass the winter in their coocoons, 
% though some appear to live on until spring in 
! ^ ie perfect state. 
fUf Other inveterate enemies of the plant-lice are eer- 
pH tain two-winged flies which belong to the order Dip- 
cl^M\ tera and family Syrphidce , of which the genus Syr- 
a, Larva of Syrphus phus is the type, or rather contains the typical species. 
fly. b, Part of a 
segment highly 
magnified. 
(See figs. 20, 41, 42 and 43). 
Tnese somewhat resemble the common house fly in 
size and shape, but are much handsomer, being usually of a bright 
yellow color, with bands and spots of black; the abdomen is flattened, 
and usually marked with bands or partial bands of black. They are 
known in some sections as “corn flies,” as they are often seen in great 
abundance, about the time the corn is in bloom, hovering around the 
stalks, poised in the air apparently almost motionless. Sometimes they 
Fig. 43. are called “sweat-flies,” from the fact that on hot, sultry 
days they are most numerous. They drop their eggs one 
in a place, upon the leaves and twigs which are infested 
with plant-lice, led by instinct to know that these will 
Syrphus larva f° rm appropriate food for their young, although they 
feeding on a as perfect insects, feed on the sweets of flowers and 
plant-louse. 0 ther similar food. The larvae which hatch from these 
plant-louse. 
are maggots without any distinct head, not even possessed of eyes, but 
compelled to seek their food by blindly exploring the surface of the 
leaf on which they are placed. They are somewhat of an elongate 
wedge shape, blunt and broadest behind, and tapering forward to the 
front. When one is feeding it elongates the front part of its body, 
and feeling around until it finds an Aphis, fastens upon it by its 
mouth, raises it in the air, and proceeds to suck the fluids from its 
body until nothing but the shell remains. 
< 
These worms or maggots, are usually of a transparent greenish color, 
sometimes more or less clouded or spotted with other colors. 
Quite a number of species belonging to this genus are found in Illi¬ 
nois, but as these have not been identified, and I am not at present 
supplied with specimens I am unable to give discretions. 
Certain minute mites, belonging probably to the genus Tronibidium , 
have also been found preying upon plant-lice, and, as I suspect, also 
upon their eggs. Some birds also assist in diminishing their num¬ 
bers. 
This array of enemies, which might be greatly increased, will show 
that nature has been careful to provide means for keeping in check 
these prolific vegetable parasities, without whose aid plants would 
necessarily soon be destroyed. 
ARTIFICIAL MEANS OF DESTRUCTION, 
The external envelope of the plant-lice is so delicate, and their hold 
on life, so far as the individual is concerned, so easily broken, that 
they are usually quite easily destroyed by the direct application of 
any acid substance to their bodies. As they live out their entire lives 
on a very limited portion of the plant they occupy, it follows that they 
