4 the COLORADO EXPERIMENT STATION 
lice is necessary to enable one to distinguish the species from one 
another or to understand the descriptions. A knowledge of the 
general habits will be of great service in enabling one to decide what 
remedies to employ for the destruction of any of these lice when 
found infesting plants in general. 
EXTERNAL structure OE THE APHIDS. 
The more important structural parts of an aphis are clearly 
shown in Fig. i. The antennae upon the head are special organs 
of touch and probably smell also. By means of them the insect 
is able to find its food plants and its mates. The cornicles, standing 
out from the posterior part of the abdomen, are little tubes through 
which the louse expels a sticky material of various colors in dif¬ 
ferent species, as green, yellow, red, black, white, etc. This secre¬ 
tion is probably for the purpose of defense against enemies, but 
these organs are never for the purpose of expelling the little clear 
drops of “honey dew” which are so eagerly sought after by ants 
and sometimes flies, bees and wasps, for food. The honey dew 
is expelled from the anal opening beneath the cauda, as shown in 
the smaller drawing. Figure 1. The beak, through which the lice 
