THE ENEMIES OF INSECTS 247 



flies, and those of numerous Neuropterous species, are 

 also important food-items. The larva? of aquatic beetles, 

 the nymphs of dragon-flies, and the case-making caddis- 

 worms are more rarely molested ; while adult water-beetles 

 and bugs appear to be almost exempt from attack. 



The foregoing paragraphs must be regarded as the 

 briefest possible outline of a very vast subject. They serve, 

 however, to emphasize the fact that insects are preyed upon 

 by myriads of creatures, great and small. In passing, it 

 is interesting to note that those who have made the food 

 of animals their special study are agreed, in the main, as 

 to the efficacy of the various protective adaptations of 

 insects. With the exception of cuckoos, few birds destroy 

 hairy caterpillars ; and although certain birds, reptiles, and 

 amphibians have acquired the knack of feeding upon 

 stinging Hymenoptera, these are sedulously avoided by 

 insectivorous creatures in general. The same remark 

 applies to those insects which emit disagreeable odours 

 and juices. 



But there are certain enemies against which insects 

 are entirely defenceless. These are the so-called insecti- 

 vorous plants, of which some five hundred species are 

 known. Most of them grow in boggy or arid soils, poor 

 in nitrogenous substances, and it is believed that this 

 deficiency has forced the plants to embark upon their 

 murderous enterprises. These plant-enemies of insects 

 capture their prey by a variety of contrivances. Among 

 the pitcher-plants the leaf, or the leaf- stalk, takes the form 

 of a hollow vessel which has been aptly described as a 

 combination of lure, pitfall, and stomach. The inner 

 walls are either intensely slippery, or else beset with 

 minute, downward-pointing hairs — devices which favour 

 the ingress of a victim, but effectually prevent its escape. 

 The lower part of the pitcher is charged with liquid, which 



