281 



and shrubs swarming with plant lice, for the powers of reproduction among the plant 

 lice are so enormous that, if unchecked by these active and efficient aids, their numbers 

 would increase to an extent at present inconceivable. In addition to those enumerated, 

 there are species belonging to some other families of beetles which, either in the larval 

 or perfect state, feed on other insects ; but the three gi-eat families named stand pre-emi- 

 nently out among the most useful of the insect tribes. 



Among the four-winged flies [Hymenoptera) we have also many active and useful 

 friends. Some of the larger species of wasps feed on insects, and many of them lay up a 

 store of insects as food for their young. When preparing for the sustenance of their 

 successors these sagacious creatures make cells in the ground, and having placed an egg 

 therein, pack the cells with a sufficient number of insects to sustain the young larva 

 when hatched until it reaches maturity. The cell, when filled, is sealed by the parent, 



and in this the insect passes through its several 

 stages of egg, larva, and chrysalis, finally escap- 

 ing from this prison-house a perfect wasp, to 

 continue its useful work. The fraternal potter 

 wasp, Eumenes fraterna (Fig. 35), is one of these 

 useful insects. All sorts of soft bodied insects 

 are stored up in these wasp cells, especially 

 caterpillars, and the wasps have the power either 

 of so poisoning their victims that they do not 

 die outright, but remain in a constant state of 

 torpor, or else they inject some fluid into their 

 bodies which preserves them, since they do not, 

 when stored in these cells, undergo decay. 



A far more important and useful family of 

 insect killers are the ichneumon flies, which belong to the same order as the wasps. 

 These active, sprightly creatures are all day long on the wing, searching everywhere, and 

 prying into every nook and corner for caterpillars, in whose bodies they deposit eggs^ 



fig. 35. 



Fig. 36. 



Fig. 37. 



puncturing the skin and placing them underneath, where they hatch into tiny grubs^ 

 which sustain themselves on the bodies of their victims, avoiding the vital organs, but 

 so weakening the caterpillars that they die either before or soon after passing into the 

 chrysalis condition. In this manner myriads of caterpillars are yearly destroyed, the 

 ichneumon usually changing to a chrysalis within the body of its victim, or spinning a 

 cocoon upon its surface. In Figs. 36 and 37 repi-esentatives of this class are shown. 



19(f. G.) 



