PARASITES. 



271 



grubs, fly maggots, etc., have their parasites ; but parasites themselves 

 are dependent upon these insects for food and become exterminated if 

 their host is exterminated. 



It is advisable not to destroy parasitic insects and when possible 

 their increase should be encouraged. This is unfortunately rarely possible, 

 but it is so when insects are collected by hand in large numbers as in 

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

 the collected larvae 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 the box or pot is carefully opened 

 in the light 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 Hymeno- 

 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, 1 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- 



Fm. 327. 



Wasp that stings caterpillars and lays them up in 

 mud nests for its young. 



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 ; 



1 Ammophila Icevigata. Sm. 



