xiv] THE ENEMIES OF SPIDERS 121 



individuals of a brood may be reared to maturity on 

 no other food than their sisters and brothers ! The 

 case of the survivor of the " Nancy Bell " in the Bab 

 Ballads would be exceedingly commonplace in the 

 aranead world. We have seen, too, how, on occasion, 

 At y pus will devour her young if they do not leave 

 the nest with due expedition. Then if the weather 

 conditions chance to be unfavourable just at the 

 period of departure from the cocoon broods are 

 liable to perish wholesale, washed away and destroyed 

 by deluges of rain ; myriads, too, must be carried out 

 to sea in the course of their ballooning operations, 

 and never come safely to land. 



But the mortality is probably even greater at a 

 still earlier stage, for hosts of spiders' eggs never 

 hatch at all, and this for two reasons. In the first 

 place, the silk of spiders is a favourite material 

 with many birds for the lining of their nests, and 

 many of them use the cocoons for this purpose. 

 Secondly, there are numerous Ichneumon flies which 

 attack and parasitise spiders' cocoons, piercing them 

 with their ovipositors and laying their eggs inside. 

 The eggs of the Ichneumon fly hatch first and feed 

 upon the eggs of the spider. Two such flies are 

 known to attack the cocoons of the garden-spider, 

 and not a single spider will emerge from a cocoon 

 thus parasitised. The spiders whose cocoons are 

 most subject to these attacks belong, as might perhaps 



