THE PROBLEM OF DEFENCE 163 



is a vision of dread to Jill the lesser denizens of the insect 

 world ; so that the caterpillar's terrifying mask probably 

 serves to scare away parasites which are bent upon its 

 destruction. The fact that ichneumons are known to 

 avoid spiders, and are seldom found in their webs, certainly 

 supports this view of the case. 



Another remarkable caterpillar is that of the puss- 

 moth {Centra vinula), which, like that of the privet hawk- 

 moth, is difficult to discover among the leaves of its food- 

 plant. When irritated, however, it immediately assumes 

 a most weird pose, and draws back its head into the first 

 body-ring in such a manner that the appearance of a 

 grotesque face is produced — the effect being heightened 

 by two intensely black spots which suggest eyes. This 

 mock face is always presented to the foe, being turned 

 from one side to the other in response to the slightest 

 touch. Further, the caterpillar is provided with a pair of 

 whip-like processes at the posterior end of its body, while 

 it is able to eject an intensely acid fluid from a special 

 gland which opens below the head. All these con- 

 trivances, while they undoubtedly serve to ward off the 

 attacks of insectivorous creatures, appear to be chiefly 

 directed against the caterpillar's most deadly enemy — 

 an ichneumon called Paniscus cephalotes. This insect 

 attempts to fix its eggs upon the caterpillar's skin, just 

 behind the head ; and when it succeeds its victim is 

 doomed. But the caterpillar is at least able to fight for 

 its life by lashing out at its foes with its flagella, or whips, 

 and squirting them with acid. 



Other insects appear to trade upon the evil reputation 

 of some well-known noxious creature. Thus, a South 

 American caterpillar mentioned by Bates startled every- 

 one to whom it was shown by its snake-like appearance ; 

 while the larva? of our own elephant hawk-moths (Chasro- 



