UTILITY OF BIRDS IN NATURE. 



19 



Fig. 12. — Host f-aterpillar, with 

 coi-oons of the parasite upou its 

 back. 



them, feed first upon the fatt^^ portions of the caterpillar 

 in which thej find themselves. The caterpillar thus unwill- 

 ingly becomes their host, furnishing them with food and 

 lodging from and within its own substance. When they 

 have made their growth, and it is nearly time for them to 

 pupate, they attack the vitals of their host, killing it, and 

 then pupating either within or upon its body. Soon they 

 emerge as perfect flies, the females 

 again seeking other caterpillars as 

 hosts for their progeny. Often 

 these parasites do not kill their 

 host until it has sought some })lace 

 of safety and pupated. Every cat- 

 erpillar or pupa thus destroyed nourishes one or man}^ of 

 these parasites, to emerge and attack surviving caterpillars. 

 The parasites themselves, however, are often attacked in the 

 same manner by a secondary parasite, which destroys them 

 precisel}' as they destroyed the caterpillar. The larger pri- 

 mary parasites may deposit a single e^^ or only a few in 

 each caterpillar, while the smaller ones may deposit the 

 entire brood in the body of a single caterpillar. 



Birds eat both predaceous and parasitic insects. We have 

 seen that they eat ground beetles, many of which are pro- 

 vided with acrid secretions that are sup})osed to render them 

 disagreeable and offensive to the taste, and so 

 give them a certain immunity from their ene- 

 mies. Evidently, however, it takes a very 

 strong flavor to take the edge off a bird's 

 appetite, for birds eat bugs ; and any child 

 who has ever eaten berries from the bushes, 

 and inadvertently put one of the berry-eating 

 bugs in his mouth, knows how disgusting their 

 Fig. 13.— Tiger flavor is. There are some useful insects that 

 beetle; a useful ^^.^ gpi(jQjjj eaten bv birds. The verv smallest 



form, eaten '' 



by very few are beneath the notice of most birds. The 



tiger beetles and some of the useful flies 



are so quick that birds find it difficult to catch them. 



AVasps and bees, though eaten by some birds, can protect 



themselves verj^ well with their stings. Probably, however. 



