CARE AND PROTECTION OF THE FOREST 129 



worms, caterpillars), and also in the egg. Thus, one of 

 the ladybird beetles was specially imported, and is used 

 by the fruit growers of California to subdue one of the 

 worst scale insects. But while these many useful hunting 

 insects undoubtedly do great service in keeping down the 

 numbers, thus preventing a real calamity of destructive 

 insects, it is chiefly the parasites, together with diseases, 

 which shorten and stamp out the insect plague when once 

 it exists. 



A typical case where a parasitic insect is making itself 

 useful to the forester is shown in Fig. 49. Here one of 

 our common ichneumon flies, by depositing its eggs on a 

 caterpillar, insures its destruction. Commonly the cater- 

 pillar is killed even before it is able to spin up or enter 

 the pupa state, and never does it get beyond this. Since 

 the ichneumons usually have more than one generation dur- 

 ing one season, their number multiplies rapidly. These 

 little wasplike insects move rapidly from caterpillar to 

 caterpillar, stinging and depositing their eggs, one or 

 several, as they go, and rarely attack a caterpillar which 

 has already be,en stung by one of their kind. In this way 

 they not only kill leaf -eating caterpillars, but attack the 

 larvae (grubs) of beetles, and thus are the best and most 

 powei^ul animal friends of the forest. 



Diseases usually help in destroying forest caterpillars 

 whenever they become very abundant. This is especially 

 true during wet seasons and in moist localities. Some of 



