187 



~. _ f Parasitic. 



(1) Insects T, -, 



v 7 l.-rredaceous. 



(2) Parasitic fungi 



(3) Insectivorous birds. 



(4) Toads, lizards, etc. 



(5) Fish. 



INSECTS AS NATURAL ENEMIES OF INSECTS. 



Insects attack and destroy other insects in two ways. 

 When it is natural for one insect to pass all or a part of its 

 life-cycle within the body of another insect, or within its 

 protective covering, as in that of scale insects, the first of 

 these is called a parasite ; while the other is called the host. 



The insect parasites of insects are numerous and ex- 

 tremely useful in reducing the numbers of injurious species. 

 They very largely belong to two orders, the Diptera and 

 the Hymenoptera. The parasitic Hymenoptera form a large 



Fig. 176. One of the parasitic hymenoptera. 

 Enlarged. {Front U.S. Dept. Agric.) 



group, and vary in size; many of them are very minute, some 

 of them so small as to be scarcelv visible to the unaided eye. 



Not all parasitic insects, however, are to be considered 

 beneficial from man's point of view, for certain of them 



