_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.