Beneficial Insects 



These parasitic larvae feed upon the blood of the host insect. The 

 host in many cases remains alive and functions naturally until the para- 

 site is fully mature. In the case of some caterpillars the parasite does 

 not emerge until after the change to the pupa has taken place. 



Some parasites live only within closely related insects. Thus certain 

 kinds are parasitic upon cutworms only, others upon grasshoppers and 

 related insects, and still others upon the eggs of certain insects. 



Since these parasites are dependent upon certain hosts for their 

 existence their numbers rise and fall with the increase and decrease of 

 their hosts. This is why some noxious insects become so numerous at 

 times. A scarcity of these insects is followed by a scarcity of their para- 

 sites. When the parasites become very few and favorable conditions 

 exist for the multiplication of a particular insect it often increases so 

 rapidly as to do much damage before the parasites again get the upper 

 hand. 



A. PREDACIOUS INSECTS 

 1. GROUND BEETLES 



(Figs. 1, 2, 3, 20, 21 and 22, Plate IX, Page 27) 



The popular name, "ground beetle," has been applied to these 

 beetles because they are most frequently encountered running rapidly 

 over the ground or lurking under stones or other objects lying on its surface. 



The majority of these beetles are shining black. However, some are 

 bright metallic green, dark blue, brown or even spotted. Their legs are 

 long and slender and their movements rapid. 



Most of the species are predacious, feeding upon other insects which 

 they capture either by pouncing upon them or by chase. Several species 

 feed upon vegetable matter, but their depredations are rarely, if ever, of 

 great economic importance. 



The larvae of ground beetles frequent the same places as the adults, 

 and, like them, are predacious. Figure 1, Plate IX, Page 27 will serve 

 as a typical example of ground beetle larvae. Figure 3, Plate IX, Page 

 27 represents a very common, black ground beetle, while Figures 20, 21 

 and 22, Plate IX, Page 27 represent the larva, pupa and adult of a 

 species already mentioned in connection with the natural control of 

 grasshoppers. 



(a) FIERY HUNTER 

 (Figs. 1 and 2, Plate IX, Page 27) 



The fiery hunter is one of our largest ground beetles and can be 

 recognized by the copper colored or golden spots on the wing covers. 

 This beetle (Fig. 2, Plate IX, Page 27) and its larva (Fig. 1, Plate IX, 

 Page 27) are particularly fond of caterpillars. By some authors it is 

 known as the "caterpillar killer." Many a cutworm has fallen a prey to 

 these beetles. 



(b) BOMBARDIER-BEETLES 



The members of one group of ground beetles are provided with a 

 sack of very volatile fluid at the tip of the abdomen. When pursued, 

 this fluid is ejected with a loud popping sound and as it comes in contact 

 with the air it is reduced to a gas which appears like a tiny puff of smoke. 

 I he sharp report accompanied by the puff of smoke-like gas suggested 

 the name "bombardier-beetles," by which these beetles are known. 



130 



