INTERRELATIONS OF INSECTS 535 
ever, the ultra-violet rays are intercepted, by means of a screen 
of sulphate of quinine or bisulphide of carbon, the ants then 
collect under the screen in preference to under the violet rays. 
From lack of experience we can form no adequate idea as 
to the range of sensation in ants or other insects. Ants can 
taste substances that we cannot, and vice versa. They show 
no response to sounds of human contrivance, yet many of them 
possess stridulating organs and organs that are doubtless audi- 
tory; whence it may be inferred that ants can communicate 
with one another by means of sounds. In rare instances the 
stridulation of an ant can impress the human ear, as in a spe- 
cies of Atta mentioned by Sharp. 
Iexperiments show that ants, as well as bees and wasps, find 
their way back to the nest, not by a mysterious “ sense of 
direction,” but by remembering the details of the surroundings, 
and in the case of ants, by means of an odor left along the 
trail. 
In studying the habits of ants, the greatest care must be 
exercised in order to discriminate between actions that may 
be regarded as purely instinctive and those that may indicate 
some degree of intelligence. If any insects show signs of in- 
telligence, the social Hymenoptera do so; but in the study of 
this recondite subject, false conclusions can be avoided only 
by observation and experiment of the most critical kind. 
Hunting Ants.—Some ants, as Formica fusca, live by the 
chase, hunting their prey singly. The African “ driver ants’ 
(Anomma arcens), although blind, hunt in immense droves, 
consuming all the animal refuse in their way, devouring all the 
insects they meet, and not hesitating to attack all kinds of ver- 
tebrates; these ants ransack houses from time to time and 
clear them of all vermin, though they themselves are a great 
nuisance to the householder. The Brazilian species of citon 
(Fig. 283, B, C) have similar habits and are lhkewise blind, or 
else have but a single lens on each side of the head. ‘These in- 
sects hunt in armies of hundreds of thousands, to the terror of 
every animate thing that they come across. They have no 
