278 A BOOK OF INSECTS 



without injury. An apparently drowned locust will revive 

 beneath the warm rays of the sun, if by chance it reaches 

 the bank or is cast on shore." 



These associations of insects for mutual advantage, or 

 for the purpose of travel, suggest the first glimmering 

 of the clannish instinct ; but no direct connection exists 

 between mere gregariousness and the true social habits 

 which have reference to the welfare of the young. Among 

 the Hymenoptera we may trace the evolution of com- 

 munism, in an ascending scale, from parental instinct in 

 its most rudimentary form. The leaf-eating larva of a 

 saw-fly is left to fend entirely for itself ; but the ichneumon 

 lays her egg in or upon the living caterpillar that is to 

 provide food for her offspring. A Scoliid wasp paralyses 

 its victim before the egg is laid. The true digger-wasps 

 go further, forming nests and storing them with cater- 

 pillars and other insects. The activities of Ammophila 

 have already been described ; while an intermediate link is 

 supplied by some of the spider-hunting wasps (Pompilidce), 

 which first capture their prey and then prepare a hole for 

 its reception. Such instances serve to illustrate the build- 

 ing up of instinct ; and among the burrowing bees the 

 progress from the solitary to the social habit is no less 

 evident. " All these insects," writes Professor Carpenter, 

 " show great care for their young, storing up food for their 

 sustenance, and building nests for their protection. In 

 most cases the food is stored, the egg laid, and the cell 

 sealed up, the mother never watching the growth of her 

 offspring. But the digger-wasp Bembex leaves the cells 

 open, and brings fresh supplies of flies to her grubs every 

 day. Here, then, we have a family life comparable to 

 that of birds. It often happens that a number of the 

 'solitary' wasps or bees . . . form their nests close 

 together, making an imperfect colony, or that a number 



