INSECTS AND BIRDS. 



269 



masses of the mantis which are often seen on bushes, 

 fences, etc., should not be destroyed, nor the mantis it- 

 self. Those delicate insects known as lace-winged flies 

 also aid greatly, for the larvae of these insects live upon 

 plant lice whenever these pests can be found. 



There are many other cannibal insects that devour 

 hordes of pests that would cause great damage if left 

 alive. 



Insect Parasites. There is another class of insects 



A TOMATO CATERPILLAR, COVERED WITH THE COCOONS OF A PARASITE 



THAT HAS KILLED IT. 

 (Photograph by M. V. Slingerland.) 



that can be considered the greatest friends of all. 

 These are the ones that actually lay their eggs, either in 

 or upon the bodies of other insects, where they hatch 

 and the young larvae feed upon the bodies of their hosts 

 finally causing the death of the latter. These are 

 known as parasites. 



Caterpillars are sometimes found upon grape or to- 

 mato vines with their backs covered all over with tiny 



