VALUE OF A KNOWLEDGE OF ENTOMOLOGY 1 3 



ladybirds^ (%• ^)> from their destruction of aphides alone, 

 ahhough some forms also do as good if not even better work 

 in limiting the numbers of scale insects. Ladybirds also devour 

 the eggs and larvae of various other insects, and especially of 

 soft-bodied forms. Several ground-beetles (fig. i8) live at the 

 expense of cutworms and other vegetable-feeding caterpillars 

 and the larvae of beetles. Of this number the great Lebia^ 

 follows the Colorado beetle wherever it goes, and appears to 



Fig. 20.— Syrphus-fly (Syrphus ribesii). a. Fly; b, lateral view of head; 

 c. larva or active immature form. All much enlarged. (Author's illustra- 

 tion, U. S. Dept. Agr.) 



have a very considerable effect in limiting its overproduction. 

 Soldier-bugs" (fig. 19) of several species attack and kill soft 

 larvae of beetles and of moths. Other important predatory 

 enemies of noxious insects are syrphus and robber flies, spiders, 

 and daddy long-legs or harvestmen. The syrphus flies* (fig. 20) 

 are particularly useful in destroying aphides. Wasps of many 

 forms provision their nests with the larvae of beetles and of 

 moths, and certain species of mites help in reducing insects of 

 pestiferous habits. 



1 Coccinellidae. 



*Lebia grandis. 



s Podlsus spp. 



* Syrphidae. 



