PARASITES. 



271 



grubs, fly maggots, oic, liavc tlicir parasites ; l)ut parasites themsolves 

 are dependent upon these insects for food and become exterminated if 

 their liost is exterminated. 



It is advisable not to destroy parasitic insects and when possible 

 their increase should be encourag-ed. Tliis is unfortunately rarely possible, 

 but it is so when insects are collected by hand in larg-e numbers as in 

 handpicking" Tur Leaf Caterpillars, or Cotton Leaf-rollers. In such cases, 

 the collected larvge and pupse should be placed in any closed receptacle, as 

 for instance, a box or an earthen pot covered with cloth. Whatever 

 parasites there are hatch out, and when tlie box or pot is carefully opened 

 in the lig*ht they fly away. As a rule the moths or butterflies that also 

 hatch fly only in the dark or are too large to escape through as small an 

 opening as the parasites can. Whenever possible it is advisable to put 

 such collected insects into a box covered by a piece of glass ; as the para- 

 sites collect on the glass, the moths hide away. If the glass is gently 

 lifted the parasites escape to continue their useful work. 



This applies also to eggs of insects, which, when collected, should 



not be burnt but placed in a vessel surrounded by water ; the insects that 



hatch from the eggs cannot escape, but the parasites can fly away. 

 The stinging predators 



are a small group of Hi/meno- 



ptera, which have instincts 



of so high an order as to 



excite the admiration of all 



who study them. We may 



describe the life of one,^ a 



common insect in the plains. 



This insect may be found in 



the fields flying among the 



plants evidently seeking for 



something. If watched with 



patience, it will be seen to 



seek for caterpillars, those 



green caterpillars so com- 

 mon on gram, tobacco, and 



other crops. Having found a large green caterpillar, it flies to it, seizes 



it, and stings it on the lower side ; the caterpillar struggles, but the wasp 



holds fast and repeatedly stings along the lower surface between the legs. 



The caterpillar then becomes motionless and is helpless ; the wasp seizes it, 



and flies off to a little distance where it has prepared a hole in the ground ; 



' ^ffimpphila Ifevigafa. Sm. 



Fia. 327. 

 Wasp that stings caterpillars and lays them up 

 mud nests for its young. 



