Size.—Vipera berus is said to reach very exceptionally a length of 2 feet 11 inches. The largest specimen in the British Museum (from Belgium) measures 2 feet 31⁄2 inches: the largest British specimen 2 feet 3 inches. Both these specimens are females. The largest male measures 2 feet 2 inches.
Distribution.—Vipera berus ranges over the whole of Northern Europe, to the extreme north of Scotland, and the sixty-seventh degree in Scandinavia, and right across Northern Asia as far east as the island of Saghalien. It is generally distributed in Great Britain, occurring also on the Isles of Arran, Islay, Skye, Lewis, and Mull, rare or absent in some districts, common in others. Its distribution in Central and Southern Europe is irregular. In Western France it does not extend much beyond the Loire to the south, only isolated captures being on record from the departments Vendée, Deux-Sèvres, Vienne, and Indre. Of rare occurrence south of Paris, in the departments Yonne and Allier and in the mountains of Auvergne, it is again abundant in some parts of the Central Plateau. To the east it is recorded from the departments Aude, Haute-Marne, and Vosges. In Belgium, it is known from Flanders, Limburg, the Meuse Valley, and the Ardennes; in Holland it is pretty generally distributed in the uncultivated parts. It is spread over nearly the whole of the German Empire with the exception of the vine districts, where it is absent or extremely rare; it is also very scarce in the mountains of the Black Forest; it is on record from only a few localities in Lorraine, and has never been found in Alsatia. In South Germany it is rarely found below 1,000 feet altitude. In Switzerland it is absent from the Jura, but occurs in the Alps chiefly between 2,500 and 9,000 feet. To the East it extends to Russia, as far north as 64°, Austria-Hungary, confined to the hills in the south, and Roumania. In the Balkan Peninsula it occurs in the mountains of Bosnia, of Herzegovina, and of Bulgaria, up to 7,000 feet. Absent from the South of France, it curiously reappears in the hills of the north coast of Spain, even at sea-level in Galicia, and in a few localities in North Portugal. On the southern side of the Alps it is much rarer than V. aspis, but it has established itself in a few low-lying districts in Lombardy, Venetia, and the neighbouring part of Emilia.
Habits.—As we see from the above sketch of its distribution, the Adder generally avoids the hotter parts of Europe; when found in the plain in the South, as in Italy, it dwells in marshy localities, and Bonaparte called it Marasso palustre (Marsh Viper) in opposition to his Marasso alpino, Vipera ursinii. In the North, however, it usually selects in preference dry moors, sandy heaths, and hills well exposed to the sun, in which, although to a certain extent a nocturnal reptile, it delights to bask. Its food is very varied: weasels, mice, voles, shrews, moles, birds, lizards, slow-worms, frogs, salamanders, large slugs, have been found in the stomach, and the very young feed also on insects and worms. Of irascible temper as a rule, Adders are very ready to bite when fresh caught, but instances are known of their becoming quite tame in captivity, allowing themselves to be handled. As a rule they refuse food in captivity, but some have been known to live for as long as five years, being fed on lizards. Accidents from their bite, although seldom heard of in this country, are of frequent occurrence in France and in Germany, where many cases of fatal results on people have been recorded.
Reproduction.—Pairing takes place in April and May, and the young, five to twenty in number, are born in August or September, exceptionally as early as the end of July; the young, on releasing themselves from the thin, transparent membrane in which they are enclosed at birth, measure 6 to 8 inches. According to J. Geithe, a black female from Saxony gave birth to seventeen young, of which only one, a male, was black.
It is probable that exceptionally some individuals pair late in the summer or in the autumn. There is a trustworthy record, by Eiffe, of three pregnant females having been caught near Hamburg on March 12, 1882, one of them giving birth to young on the following day.
Dicephalous young have occasionally been observed. One 6 inches long was found crawling in a field near Hornburg in Germany in October, 1895, and, having been kept alive for some time, was observed to hiss and open the two mouths alternately when taking up a defensive attitude. Another similar monster, from Cornwall, is reported to have been sent alive to the London Zoological Gardens in 1854.
24. Vipera aspis, Linnæus
The Asp Viper
Form.—Rather more elongate than in the preceding. Snout flat above, more or less distinctly turned up at the end, with sharp, not or but very slightly raised canthus, and vertical or nearly vertical loreal region. Vertical diameter of the eye equal to or a little less than its distance from the mouth. The raised upper border of the transversely truncate or obtusely pointed extremity of the snout, coupled with the downward slant of the supraocular region and canthus rostralis, gives the head, seen from the side, a peculiar expression; the eye is so oblique that a vertical line drawn from the posterior extremity of the supraocular shield to the lip usually passes through the eye or down its posterior border; but the extent to which the snout is turned up at the end varies considerably, some specimens approaching V. berus in this respect, others V. latastii. Length of tail five and a half to eight times in total length in males, seven to nine times in females.
