M. Huber, initiated in the mysteries of the life of these insects, and whose observations can be most relied on, has made us acquainted with two of their maladies: one is a species of vertigo, occasioned, as he thinks, by a too great heat of the sun, and which transforms them for two or three minutes into a sort of bacchantes; the other malady, much more severe, causes them to lose the faculty of directing themselves in a right line. These Ants turn in a very narrow circle, and always in the same direction. A virgin female, inclosed in a sand-box, and attacked by this mania, made a thousand turns by the hour, describing a circle of about an inch in diameter; it continued this operation for seven days, and even during the night.[570] Immense swarms of winged Ants are occasionally met with, and some have been recorded of such prodigious density and magnitude as to darken the air like a thick cloud, and to cover the ground or water for a considerable extent where they settled. We find in the memoirs of the Berlin Academy a description of a remarkable swarm, observed by M. Gleditch, which from afar produced an effect somewhat similar to that of an Aurora Borealis, when, from the edge of the cloud, shoot forth by jets many columns of flame and vapor, many rays like lightning, but without its brilliancy. Columns of Ants were coming and going here and there, but always rising upward, with inconceivable rapidity. They appeared to raise themselves above the clouds, to thicken there, and become more and more obscure. Other columns followed the preceding, raised themselves in like manner, shooting forth many times with equal swiftness, or mounting one after the other. Each column resembled a very slender net-work, and exhibited a tremulous, undulating, and serpentine motion. It was composed of an innumerable multitude of little winged insects, altogether black, which were continually ascending and descending in an irregular manner.[571] A similar kind of Ants is spoken of by Mr. Accolutte, a clergyman of Breslau, which resembled columns of smoke, and which fell on the churches and tops of the houses, where they could be gathered by handfuls. In the German _Ephemerides_, Dr. Chas. Rayger gives an account of a large swarm which crossed over the town of Posen, and was directing its course toward the Danube. The whole town was strewed with Ants, so that it was impossible to walk without crushing thirty or forty at every step. And more recently, Mr. Dorthes, in the _Journal de Physique_ for 1790, relates the appearance of a similar phenomenon at Montpellier. The shoals moved about in different directions, having a singular intestine motion in each column, and also a general motion of rotation. About sunset all fell to the ground, and, on examining them, they were found to belong to the _Formica nigra_ of Linnæus.[572]