PASSIVE DEFENCE 347 



as well as fruit trees. Before this time procession caterpillars were 

 not wanting from the Hanau district, but the large number of 

 bats flying about in the night had caught and devoured so many- 

 moths that great increase of this pest was prevented. When 

 almost all the bats in the district had been destroyed, a great 

 caterpillar infestation could not be avoided, the insect being freed 

 from almost all its enemies. For the mature winged stage is of 

 nocturnal habit, and exposed only to the attacks of bats and 

 goatsuckers, the latter never being present in more than limited 

 numbers. The caterpillars are so well protected with hairs that 

 scarcely anything but cuckoos can devour them, and the chrysa- 

 lides are sheltered by a thick cocoon from the attacks of most 

 enemies. The eggs alone are largely eaten during the winter by 

 gipsy migrants (tits, tree-creepers, nuthatches, &c.). The pro- 

 cession-moth, in fact, has always so few enemies, that it invariably 

 increases largely in numbers if the chief of them happens to be 

 rapidly exterminated." (Extracted from Gloger, by Ritzema Bos, 

 in A7iimal Friends and Foes.) 



