INSECTS. 317 



order, containing many species, and these are composed 

 of very numerous individuals. Flies and mosquitos are 

 exceedingly annoying to man and animals, and many spe- 

 cies, in the larval state, consume vegetable matters ; but 

 even here they are often of use in consuming decayed 

 vegetation, and like many others of the order may be con- 

 sidered scavengers, consuming, as they do, immense quan- 

 tities of filth and carrion, that would otherwise continue 

 to taint the air and produce disease. 



Some of the most destructive insects of this order are 

 the Gall-gnats, among which are the Wheat-fly and the 

 Hessian-fly, which often sadly interfere with the farmer's 

 prospects. 



A few insects will now be noticed more in detail. 



Selaildria cerasi, or Blennocampa cerasi, is the com- 

 mon Slug of the cherry and pear trees, and quite a trouble- 

 some hymenopterous insect. In some parts of the United 

 States these little creatures are so numerous as to strip 

 the substance from the foliage of pears and cherries. 



Our Slug resembles the Selandria cethiops of Europe, 

 but is declared to be diflerent. The larvas are at first 

 white, but the slimy substance that oozes from their bodies 

 covers them with an olive coating. They have twenty 

 very short legs ; when fully grown, the largest are about 

 nineteen-twentieths of an inch long. The head is con- 

 cealed under the fore part of the body, which is largest 

 before, and tapers behind. They attain their growth in 

 twenty days, casting their skins five times, eating them 

 until the last time, after which they remain free from vis- 

 cidity, and are of a clear yellow color. They leave the 

 tree and enter the ground to the depth of one or three 



