SPIDERS 169 



their eggs are eaten by hosts of different kinds of animals. In this 

 country the most important of these are probably toads and frogs, 

 starlings and other insectivorous birds, shrews, wasps and centi- 

 pedes. Invertebrate enemies are very much more numerous and 

 probably destroy larger numbers of spiders than do vertebrates, 

 but spiders enter largely into the diet of smaller birds, being fed 

 especially to the nestlings. Moreover, many species of birds use 

 spiders' egg cocoons to line their nests. 



Social wasps often kill spiders to feed their larvae, and there are 

 two British families of solitary digger wasps, the Pompilidae and 

 Trypoxylinidae, which hunt spiders. The spiders are paralysed by 

 stings, often in the principal nerve ganglia and are then dragged to 

 previously prepared cells or burrows. After this the wasp lays an 

 egg on each carcass and other paralysed spiders are added before 

 the burrow is sealed up. These must provide enough food for the 

 wasp grub, when it hatches, to last throughout the whole of its 

 larval development, for the mother wasp never sees her offspring. 

 Fabre, Kingston and other naturalists have written graphic ac- 

 counts of the habits of spider-hunting wasps. All kinds of spiders 

 are attacked, although wolf spiders are perhaps the most frequent 

 victims of the Pompilidae, and in the tropics even large Thera- 

 phosidae fall prey to these terrible foes. The first action of one of 

 these wasps when it attacks a spider is to remove the latter from its 

 environment, for a garden spider is much more vulnerable when 

 torn away from its web and a burrowing spider dragged into the 

 open is nearly defenceless. It has been observed, however, that 

 spiders appear completely 'panic-stricken' when confronted by a 

 fossorial wasp. Their immediate reaction seems to be to flee, and 

 they do not try to defend themselves even when cornered. 



The parasites of spiders include Protozoa and Nematoda, but 

 there are few records in the literature. Infinitely more important, 

 especially in tropical climates, are 'parasitoids' or lethal parasites, 

 particularly of the family Ichneumonidae. These insects probably 

 paralyse a spider by means of their sting before laying an egg on its 

 back. Although the most frequent victims of spider parasites are 

 web-spinners, several different kinds of hunting spider have also 

 been found with eggs or larvae on their backs. These larvae even- 

 tually cause the death of their victim by feeding on the contents of 



