368 



OUR INSECT FRIENDS 



forms of scavengers: The burying beetles remove carrion, offen- 

 sive both to the eye and nose. The flesh fly larvae and others 

 devour meat which either is or will be putrid. Pomace flies feed 

 upon decaying fruit. Flies and beetles which breed in and feed 

 upon excrement should also be regarded as, in a way, beneficial. 



(d) As plant pollinators many insects are of invaluable assist- 

 ance to man, cross-fertilizing many varieties of fruit which might 

 ordinarily be sterile. 



Parasitic Insects. Of all beneficial forms, however, the para- 

 sitic insects, from an economic standpoint, are the most important, 



FIG. 373. Red-tailed tachina fly, one of the Tachinidw; a, fly natural size; b, fly en- 

 larged; c, army worm, natural size, upon which eggs have been laid; d, parasitized army 

 worms, enlarged. (After Slingerland.) 



and so highly is their work against injurious forms appreciated 

 that in many instances our government has gone to the expense 

 of importing not only "lady beetles," or Coccinellids, which 

 belong to the predaceous group, but large numbers of parasites 

 which materially reduce the ranks of the various injurious forms 

 upon which they prey. Rearing parasites for economic use has 

 been found practical in this country. 



Parasites on Parasites. It is to be noted, however, that many 

 of these parasites are in turn themselves parasitized, their 

 parasites being referred to as secondary parasites. Even the second- 

 ary parasites are frequently the victims of tertiary parasites, and 



