102 THE BIOLOGY OF INSECTS 



No doubt can be felt that a very large proportion of an 

 insect's normal activities are instinctive, in that they result 

 from a set of complicated reflexes, while they serve to ensure 

 the survival either of the individual or of the race. This is 

 especially evident in modes of behaviour concerned with 

 reproduction and growth among insects whose manner of 

 life when adult diflfers from that in the early stages of their 

 life-history. The actions that accompany egg-laying by a 

 female moth or digging- wasp, for example, are all directed 

 towards the provision of environment and food suitable for 

 the larva. The moth, herself a feeder on the nectar of 

 flowers which she sucks, lays her eggs on the leaf of a plant — 

 often of some one definite species — which the caterpillar 

 will devour. Either the plant provides a stimulus to egg- 

 laying through the senses of smell or sight and the act is 

 instinctive, or the moth remembers how she fed when she 

 was a caterpillar and provides for her young accordingly. 

 No student of insect behaviour would seriously suggest the 

 second alternative as probable, and we feel compelled to 

 accept the first. A digging-wasp makes a nest, usually by 

 excavating a pit in the ground, and either before or after 

 this labour, hunts for prey to bury along with her eggs so as 

 to ensure a supply of food for her grubs. In most cases 

 that have been carefully observed, the behaviour of the 

 mother insect is so uniform that she may be said to follow 

 a definite routine, each step in the process apparently 

 suggesting the next, so that nothing is done out of its 

 regular order. Some observations of G. W. and E. G. 

 Peckham (1898) are of great interest in this connection. 

 Some American species of Pompilus, studied by them, 

 capture spiders to serve as food for the grubs ; the female 

 wasp paralyses the spider with her sting, then places it with 

 its waist in the fork of a plant-shoot, so that it will not fall, 

 and then proceeds to dig the hole for her nest. Wishing to 

 observe carefully how the wasp stings the spider, the 

 Peckhams on one occasion removed from its place on a bean 

 plant the paralysed spider which a female Pompilus had 

 just put there, and substituted an uninjured spider. The 



