Sec. 12.] 



ENTOMOLOGICAL. 



245 



quantity of the soil tlirougli which they burrow, extract from it a great part of 

 tlie decaying vegetable matter it may contain, and eject the rest in a finely 

 divided state. In this manner a field manured with marl has become 

 covered, in the course of SO years, with a bed of earth averaging 13 inches 

 in thickness." 



White, in his " Natural History of Selborne," savs : 



" Worms seein to be great pi-omoters of vegetation, which would proceed 

 I)ut slowly without them, by boring, perforating, and loosening the soil and 

 rendering it pervious to rains and fibers of plants, by drawing straws and 

 stalks of leaves and twigs into it, and most of all, by throwing up such 

 infinite numbers of lumps of earth, called worm-casts, which, being their 

 excrement, is a fine manure for grain and grass." 



It is a part of the system of comminution spoken of under another liead ; 

 and if all the earth could be eaten by worms, it would serve as a manure for 

 crops, simply because it had been pulverized, and thereby fitted for their 

 use. 



Some time since, in company with several gentlemen, we listened to a 

 conversation with reference to the value of the cai'tli-worm, one gentleman 

 claiming that they were a nuisance in the garden, and others asserting that 

 they were a great blessing, as mole drainers, and always an index of the 

 fertility of the soil. Here is a paragraph from the Encyclopedia Br'tinn- 

 nic'is right to the point : 



"Tlie common earth-worm, though apt to be despised and trodden on, is 

 really a useful creature in its way. Mr. Knapp describes it as the natural 

 manurer of the soil, consuming on the surface the softer part of decayed 

 vegetable matter, and conveying downward the more woody fibers, which 

 there molder and fertilize." 



271. Plailt-Licc l)«'s(royprSi — Tliere is an ichneumon fly, a yory small 

 blackish insect with yellowish legs and abdomen, not (piite the twentieth of 

 an inch long, which destroys myriads of aphides. The female lays an egg in 

 each louse, and the grub from that devours its nest, leaving only the skin 

 attached to the leaf, serving for a shelter for the larva in its jiupa state. The 

 fly comes out of a hole in the louse's back, and repeats the oiieration. 

 Careful examination will disclose a great many of these perforated empty 

 aphis skins upon plants that would be entin-ly destroyed by along-continued 

 multi[)lication of their consumers, but t'or this little parasite. 



The Syrphns is the name of another destroyer of the aphis that abounds 

 upon collon-plants. Tliis is not a parasite; the vf^g;& being laid on the leaf 

 among the aphis, the maggot, which is, when full grown, about one fifth uf 

 an inch long, makes its food of the lice. The jjupa is formed on the leaf, in 

 a case made by the worm of a glutinous secretion — the juices it has sucked 

 out of the lice it fed upon. The fly is seven tenths of an inch across the 

 wings, which are double ; the body appearing like a diminutive wasp, banded 

 with brown, black, and yellow. It hovers much on the wing, without much 

 motion, unless disturbed, when it shows its power of swift flight. This 



