THE HOUSE FLY. (Musca domestica.)
This insect lays its eggs in sinks, dunghills, or any other place where there is decaying vegetable matter tolerably moist. The larvæ, or maggots, are thick and fleshy, without legs, but having the mouth furnished with hooks, by means of which they drag themselves along when they wish to move. They go into the pupa state without throwing off the skin of the maggot; and when the perfect insect appears, it forces off a kind of cap from one end of the pupa case, in order to make its escape. The Blue Bottle flies (Musca erythrocephala and Vomitoria) are only too well known from their habit of depositing their eggs upon our meat in summer. In the Flesh fly (Musca or Sarcophaga carnaria) and some allied species, the eggs are hatched within the body of the parent, which thus deposits living larvæ upon the decomposing animal matter that constitutes their food. These flies are so prolific and their larvæ so voracious that Linnæus says the progeny of them would devour a horse as quickly as a lion could do it.
THE GNAT. (Culex pipiens.)
This is an insect which deserves the observation of the naturalist, not only for the very curious conformation of its proboscis (which so quickly and powerfully penetrates into our skin, and through which it sucks our blood into its body), but also for the several metamorphoses it undergoes before it arrives at its winged state. The Gnat deposits its eggs upon the surface of stagnant water, and sets them upright one against another, in the form of a small boat: after floating upon the water for several days, as soon as the time of hatching arrives the larvæ, which the eggs contain, escape into the water in which they swim about with vigorous jerking movements. They are compelled to visit the surface to take in a supply of air, and for this purpose the tail is furnished with a short tube, surrounded at its extremity with a star of bristles, which, when spread out, prevent the water from flowing into the air tube. The change to the pupa state is a curious one. In this condition the insect exhibits a rather slender body with a bulky anterior extremity, in which the head, wings, and limbs are enclosed; the tail is furnished with a pair of leaves or membranous plates, the matting tube has vanished from this part and in place of it we find two tubes situated on the sides of the thorax: having passed about ten days in this state, its increase being at an end, it keeps longer near the surface, and at last the outer skin bursts, and the winged insect, standing upon the exuviæ it is going to leave behind, smooths its new-born wings, springs into the air, and begins its depredations. The fecundity of the Gnat is so remarkable, that in the course of one summer they might increase to the amazing number of five or six hundred thousands, if Providence had not ordered that they should become the prey of birds, who by this means prevent their multiplying more than they generally do. These insects are very annoying from their blood-sucking propensities; and as the sucker is horny at the tip, it inflicts a severe wound, into which the insect emits a small quantity of poison, which occasions the pain and inflammation always felt from a Gnat bite.
Order VIII. Suctoria.
These insects are without wings. The mouth is furnished with a trunk or beak, formed to wound as well as to suck.