86 INSECTS 



animals of many species, birds and, last but by no means 

 least, in the war of insect upon insect, the predatory 

 and parasitic forms. It was almost inevitable that 

 in the course of development some originally plant- 

 feeding insect would find itself in position to get its 

 plant juices at second hand, so that, instead of feeding 

 upon plant tissue directly, it fed upon its next neighbor 

 and got the same material indirectly. We have, even 

 now, examples in Hemiptera and Coleoptera of species 

 that feed upon vegetable tissue and also upon other 

 insects when they get in the way; or of species which, 

 while normally predatory, occasionally feed upon 

 vegetation. In the Hemiptera I know of examples of 

 this kind in the Pentatomida and in Coleoptera they 

 occur in the Carabidce and Coccinellidce. And the 

 step from predatory to parasitic habits is an easy one, 

 albeit a much greater specialization. Insect feeders 

 upon vegetable life were first developed; predatory 

 forms came very soon afterward and occur in almost 

 if not quite all orders; parasitism on other insects 

 came much later, and is best developed in the highest 

 and most specialized orders, being practically non- 

 existent in the lower or primitive types. Parasites 

 on higher animals, such as the biting and sucking lice 

 which occur in the Neuroptera and Hemiptera, are not 

 in any way comparable with the insect parasites that 

 occur in the Hymenoptera and Diptera, to which highly 

 specialized and most recently developed orders the 

 great majority of all the parasites on insect life belong. 

 There are few true parasites in any other of the orders. 

 Among the Thysanura we have no parasites and no 

 predatory forms. In the Neuroptera we have many 

 decidedly predatory forms and the beginnings of par- 

 asitism. The Neuroptera as limited in Chapter I, con- 

 sists of a number of remnants of earlier types, agreeing 



