There is an animal,[149] also, that is generated in the summer, which has its head always buried deep in the skin [of a beast], and so, living on its blood, swells to a large size. This is the only living creature that has no outlet[150] for its food; hence, when it has overgorged itself, it bursts asunder, and thus its very aliment is made the cause of its death. This insect never breeds on beasts of burden, but is very commonly seen on oxen, and sometimes on dogs, which, indeed, are subject to every species of vermin. With sheep and goats, it is the only parasite. The thirst, too, for blood displayed by leeches, which we find in marshy waters, is no less singular; for these will thrust the entire head into the flesh in quest of it. There is a winged insect[151] which peculiarly infests dogs, and more especially attacks them with its sting about the ears, where they are unable to defend themselves with their teeth. CHAP. 41. (35.)—MOTHS, CANTHARIDES, GNATS—AN INSECT THAT BREEDS IN THE SNOW. Dust, too, is productive of worms[152] in wools and cloths, and this more especially if a spider should happen to be enclosed in them: for, being sensible of thirst, it sucks up all the moisture, and thereby increases the dryness of the material. These will breed in paper also. There is one kind which carries with it its husk, in the same manner as the snail, only that the feet are to be seen. If deprived of it, it does not survive; and when it is fully developed, the insect becomes a chrysalis. The wild fig-tree produces gnats,[153] known as “ficarii;” and the little grubs of the fig-tree, the pear-tree, the pine, the wild rose, and the common rose produce cantharides,[154] when fully developed. These insects, which are venomous, carry with them their antidote; for their wings are useful in medicine,[155] while the rest of the body is deadly. Again, liquids turned sour will produce other kinds of gnats, and white grubs are to be found in snow that has lain long on the ground, while those that lie above are of a reddish[156] colour—indeed, the snow itself becomes red after it has lain some time on the ground. These grubs are covered with a sort of hair, are of a rather large size, and in a state of torpor. CHAP. 42. (36.)—AN ANIMAL FOUND IN FIRE—THE PYRALLIS OR PYRAUSTA. That element, also, which is so destructive to matter, produces certain animals; for in the copper-smelting furnaces of Cyprus, in the very midst of the fire, there is to be seen flying about a four-footed animal with wings, the size of a large fly: this creature is called the “pyrallis,” and by some the “pyrausta.” So long as it remains in the fire it will live, but if it comes out and flies a little distance from it, it will instantly die. CHAP. 43.—THE ANIMAL CALLED HEMEROBION.