ORDER VI. VEIN-WINGED INSECTS. 243 



All the insects of this order thus far enumerated are 

 more or less useful to man, by their agency in the destruc- 

 tion of such a vast number of caterpillars, grubs, and other 

 insects directly injurious to vegetation. But we must men- 

 tion one family of the ichneumons that are as destructive to 

 vegetation as they are to the caterpillars, viz., that com- 

 posed of the several genera of the Saw-wasp. 



Now there is one fact in connection with the larvae of this 

 family which should be mentioned in the beginning. The 

 true caterpillars, which are metamorphosed into moths and 

 butterflies, never have more than sixteen legs ; but many 

 of these larvae are found which almost exactly resemble 

 caterpillars in appearance, but which have more than eight 

 pairs of legs, and these are called pseudo or false caterpil- 

 lars, because they do not transform into lepidoptera, but 

 into hymenopterous insects. 



Formerly, many experienced naturalists held the opinion 

 that all the wasps which they found issuing from the co- 

 coons spun by these pseudo-caterpillars were the produc- 

 tion of ichneumons ; but more extensive and closer investi- 

 gations proved this to be an error. The pseudo-caterpillars 

 proceed from eggs deposited by different species of hymen- 

 optera, and each propagate their own species, some being 

 ichneumons, others very diflferent species of wasps. Those 

 which feed on leaves deposit their eggs on them, while other 

 wasps, which feed on wood, deposit their eggs under the bark 

 of trees. When fully grown, most of the caterpillars go to the 

 ground, and transform themselves into cocoons under its sur- 

 face. None of these wasps are provided with a venomous sting. 



Notwithstanding the pseudo -caterpillars, like the true 

 ones, are ornamented with a great variety of colors, cast 

 their skin four times, and spin silky cocoons, yet they may 

 be recognized as false by their globular brown or black 

 head, and by the number of their feet, which sometimes is 

 eighteen, sometimes twenty, and even twenty-two. 



