146 HEREDITARY CHARACTERS 



wasp first makes a nest, then drags the prey into it and 

 lays her egg or eggs upon the animals which are destined 

 to provide food for the larvae when they hatch out. The 

 female then seals up the nest and does not visit it again. 

 Now, in providing the food supply for the future larvae, 

 several extraordinary instincts come into play. It is neces- 

 sary that the caterpillars, crickets, and grasshoppers should 

 be paralysed when they are caught, otherwise the wasp 

 would have tremendous difficulty in conveying them to 

 her nest, for frequently the prey is much larger than the 

 wasp. Again, when the larvae are hatched out, they are 

 very delicate in structure, and if these comparatively large 

 animals were able to move about freely they would probably 

 kill the larvae instead of providing them with food. On the 

 other hand, if the prey were killed outright by the wasp 

 when caught, decomposition would set in in a few hours, 

 and thus the provision made by the female wasp would 

 be useless to the larvae. This difficulty is, however, over- 

 come by the wasp. When Ammophila catches a cater- 

 pillar she stings it in each of the segments of the body. 

 In the caterpillar there is a separate nervous centre 

 (ganglion) in each segment, and if only one or two were 

 stung, the other segments would still be able to move 

 quite freely. In the prey of Sphex, however grasshoppers 

 and crickets there are three separate nervous centres 

 (ganglia) which control the movements of the animal. 

 These are situated in the thorax, and when the Sphex 

 catches her prey she stings it in these three separate 

 ganglia. The result of this is that the prey is rendered 

 unable to move, but is not killed. Fabre, who first de- 

 scribed these phenomena, 1 was at first unable to understand 

 how it was that the prey he found in the nests of these 

 fossorial wasps did not decay, but he subsequently showed 

 exactly what happened by some very ingenious experiments. 



1 Fabre, J. H., Souvenirs Entomologiques, Paris. English translation of first 

 series Insect Life (Macmillan, London, 1901) contains account of Ammophila 

 and Sphex. 



