INTERRELATIONS OF INSECTS 335 



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. 



Experiments 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 Eciton 

 (Fig. 283, B, C) have similar habits and are likewise 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 



