INSECTS. 113 



Some insects, such as lice and flies, make a living 

 by sucking blood out of other animals. Such 

 creatures are called parasites^ Insects, too, have 

 parasites that either suck or eat away their vitality. 

 Many ground beetles are literally covered with lice 

 which can easily be seen with the naked eye. 

 The common house-fly has a similar enemy, also a 

 fungus growth that carries off large numbers of 

 them toward the close of summer. 



The ichneumon fly probably does as much, or 

 more damage to insect life than does any other 

 creature. It is provided with organs by means of 

 which it pierces holes in the bodies of caterpillars 

 and deposits its eggs therein. These eggs soon 

 hatch and the young ichneumons slowly but gradu- 

 ally eat away the internal soft parts of their host. 

 The caterpillar eats voraciously to supply the 

 waste, but to no effect. When the ichneumons are 

 ready to come out into the world to lead a winged 

 life, they finally eat the vital organs of the cater- 

 pillar, leaving nothing but the empty outer shell. 

 A similar fate overtakes large numbers of army 

 worms and grasshoppers. 



A large kind of ichneumon has piercing or 

 rather, drilling organs several inches long. With 

 these it is able to drill holes deep into the trunks 

 of trees to the burrows of wood-boring grubs, upon 

 which the young feed. It can be safely said that 

 ichneumon flies help to keep down the numbers of 

 injurious insects, and are therefore man's friends. 



