UTILITY OF BIRDS IN NATURE. 19 



them, feed first upon the fatty portions of the caterpillar 

 in which they 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 , 



r Fig. 12. — Host caterpillar, with 



host until it has SOUght Some place cocoons of the parasite upon its 



of safety and pupated. Every cat- "" ' 

 erpillar or pupa thus destroyed nourishes one or many 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 

 precisely as they destroyed the caterpillar. The larger pri- 

 mary parasites may deposit a single egg 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 supposed 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 are se i(j oin eaten by birds. The very smallest 



form, eaten J / 



by very few are beneath the notice of most birds, lne 



birds - tiger beetles and some of the useful 'flies 



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



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



themselves very well with their stings. Probably, however, 



