12 INSECTS INJURIOUS TO VEGETATION. 



In the adult state these insects live chiefly on the honey and pollen of 

 flowers, and the juices of fruits. The larvae of the saw-flies ( TenUire- 

 ditiidce), under the form of false-caterpillars and slugs, are leaf-eaters, 

 and are oftentimes productive of much injury to plants. The larvae of 

 the xiphydrians (Xiphydriadcr), and of the horn-tails (UroceridcB), are 

 borers and wood-eaters, and consequently injurious to the plants inhab- 

 ited by them. Pines and firs suffer most from their attacks. Some of 

 the warty excrescences on the leaves and stems of plants, such as oak- 

 apples, gall-nuts, and the like, arise from the punctures of four-winged 

 gall-flies {Diplolepididcr), and the irritation produced by their larvse, 

 which reside in these swellings. The injury caused by them is, com- 

 paratively, of very little importance, while, on the other hand, we are 

 greatly indebted to these insects for the gall-nuts that are extensively 

 used in coloring, and in medicine, and form the chief ingredient in ink. 

 We may, therefore, write down these insects among the benefactors of 

 the human race. Immense numbers of caterpillars and other noxious 

 insects are preyed upon by internal enemies, the larvse of the ichneumon- 

 flies {Ei'aniad<2, Ichneumonida, and ChaJcididcc), which live upon the 

 fat of their victims, and finally destroy them. Some of these ichneumon- 

 flics (Ichneumones oi-idorinu*) are extremely small, and confine their 

 attacks to the eggs of other insects, which they puncture, and the little 

 creatures produced from the latter find a sufficient quantity of food to 

 supply all their wants within the larger eggs they occupy. The ruby- 

 tails [Chrysidida), nud the cuckoo-bees (HylcBus, Sphecodes, Nomada, 

 Melecta, Epeolus, Ccelioxys,Vind Stelis), lay their eggs in the provisioned 

 nests of other insects, whose young are robbed of their food by the 

 earlier hatched intruders, and are consequently starved to death. The 

 wood-wasps (CraZiro?JiVZ(r), and numerous kinds of sand-wasps (Larradcp, 

 Bemhicido', Sphegida, Pompilido'^ and Scoliadce), mud-wasps (Pelo- 

 p(vus), the stinging velvet-ants (Ahitilladcp), and the solitary wasps 

 (Odynerus and Eiwicnes), are predaceous in their habits, and provision 

 their nests with other insects, which serve for food to their young. The 

 food of ants consists of animal and vegetable juices; and though these 

 industrious little animals sometimes prove troublesome by their fondness 

 for sweets, yet, as they seize and destroy many insects also, their occa- 

 sional trespasses may well be forgiven. Even the proverbially irritable 

 paper-making wasps and hornets (Polistes and Vespa), are not without 

 their use in the economy of nature ; for they feed their tender ofl^spring 



* Now placed among the Proctotrupidce. 



