France they are called Bêtes de la Vierge, or Vaches à Dieu, as if under the tutelary patronage of the Virgin herself. But they really deserve all the protection they receive, for while they leave our hops and valuable plants uninjured, they destroy the greatest enemy of these vegetables-the plant-louse. "If," says Kirby, we could only discover a mode of increasing these insects at will, we might not only, as Dr. Darwin has suggested, clear our hot-houses of aphides by their means, but render our crops of hops much more certain than they now are." In 1827, the shore at Brighton, and all the watering places on the south coast, were literally covered with them, to the terror of the inhabitants: they being ignorant that these insects were emigrating after having cleared the neighbouring hop-grounds of the destructive aphis. It furnishes a subject of serious consideration, as well as an argument for a special providence, to know, that the accurate Reaumur, and other naturalists, have observed, that when any kind of insect has increased inordinately, their natural enemies have increased in the same proportion, and thus preserved the balance. VOL. I. CHAPTER XI. Gnat-Bug-Fly-bug-Flea-Chigoe-Louse-Mites and Ticks-Gad-fly. THERE are few insects with whose form we are better acquainted than that of the gnat. It is to be found in all latitudes and climates; as prolific in the Polar as in the Equatorial regions. In 1736 they were so numerous, and were seen to rise in such clouds from Salisbury cathedral, that they looked like columns of smoke, and frightened the people, who thought the building was on fire. In 1766, they appeared at Oxford, in the form of a thick black cloud; six columns were observed to ascend the height of fifty or sixty feet. Their bite was at tended with alarming inflammation. To some ap pearances of this kind, our great poet Spenser alludes, in the following beautiful simile: As when a swarm of gnats at eventide, Their murmurring small trumpets sownden wide, In Lapland, their numbers have been compared to a flight of snow when the flakes fall thickest, and the minor evil of being nearly suffocated by smoke is en dured to get rid of these little pests. Captain Stedman says, that he and his soldiers were so tormented by gnats in America, that they were obliged to dig holes in the ground with their bayonets, and thrust their heads into them for protection and sleep. Humboldt states, that "between the little harbour of Higuerote and the mouth of the RioUnare, the wretched inhabitants are accustomed to stretch themselves on the ground, and pass the night buried in the sand three or four inches deep, exposing only the head, which they cover with a handkerchief." After enumerating these and other examples of the achievements of the gnat and mosquito tribe, Kirby says, "It is not therefore incredible that Sapor, King of Persia, should have been compelled to raise the siege of Nisibis by a plague of gnats, which attacked his elephants and beasts of burden, and so caused the rout of his army; nor that the inhabitants of various cities should, by an extraordinary multiplication of this plague, have been compelled to desert them; nor that, by their power of doing mischief, like other conquerors who have been the torment of the human race, they should have attained to fame, and have given their name to bays, towns, and territories *." The instrument with which they inflict their tortures, simple as it appears to the eye, is nevertheless wonderfully complicated and ingenious: it forms a set of lancets, consisting of five pieces, inclosed in a case. This case is split from one end to the other, Mosquito Bay. Mosquitas, a town in Cuba. Mosquito country in North America. and, as the creature sucks, it serves to give steadiness to the instruments, while they are thrust forward into our flesh. In the first figure (fig. 1) the lancets alone are seen entering, and their case forms an arc, supporting them. In the second (fig. 2), the lancets are perceived to have penetrated more deeply, while the case, not entering, is seen to form an angle. In order to see the whole process of suction, Reaumur courted what most others sedulously shun—a sting or two: "After a gnat had done me the kind 2 ness of settling on the hand I stretched out, I saw that it protruded a very fine point from its proboscis, with the extremity of which it felt four or five spots of my skin. It would appear that it knows where it can pierce through most easily, and reach a large blood vessel. Having selected a spot for its operations, it soon causes the sufferer to feel its sting." The fine point when magnified presents the following formidable picture, of which some of the detached pieces seem admirably fitted for the gnat's purpose and our an 2 1 3 noyance. It is not, however, the introduction of these points, which, when combined, are as much less in size than the finest needle, as that is than a sword, that causes the irritation which, when extended over the limb, has in some cases rendered amputation necessary-the_gnat introduces a little liquid, for the purpose, as Reaumur conjectures, of rendering our thick blood thin enough to be sucked through its proboscis. To allay the effects of this poison, there seems to be no better or readier means than sweet oil, which, if applied to the wound within a few hours after it has been made, will remove the swelling, although when delayed five or six hours it has not effect. The gnat undergoes many metamorphoses. If water be allowed for some time to stand still in a bucket, or if a quantity of that fluid be taken from a stagnant pool, it will be found to contain innumerable aquatic insects of the following shape (fig. 1): these are the larvæ of the gnat; they swim with the head downwards, a position which, to most anmals, would be fatal; they retain the longest tube, which is their respiratory organ, on the surface: the other tube forms the anus. In 2 3 1 |