122 MOUNTAIN AND MOORLAND 



Andrew's cross of black or dark brown on the top of 

 the head and a zigzag" dark band along the middle 

 line of the back. An Adder two feet long is a large 

 specimen. 



There are many facts about the Adder that are 



significant from our general natural history point of 



view. It is the only poisonous snake in Britain, the 



Grass Snake (Tropidonotus nairix) and the Smooth 



Snake (Coronella lavis) being quite innocent. As it 



is widely distributed throughout Europe and yet does 



not occur in Ireland, the probability is that it colonised 



Great Britain after Ireland had been separated off, 



and while the land connection between Great Britain 



and the Continent was still in existence. That there 



should be so few snakes altogether in Britain is to be 



connected with the fact that they are coldblooded 



animals, tending to take on the temperature of their 



surroundings and thus ill suited for countries that are 



very cold in winter. The Adder has a constitution 



well suited to stand cold, for it is found on the Alps 



up to 6,000 feet; but, whether on mountain or low 



ground, it passes into winter lethargy for a variable 



number of months according to the severity of the 



conditions. It sinks into a state of "suspended 



animation," and the risks of the cold are lessened by 



the reduction of activity to a minimum. We think it 



useful to keep the term "hibernation" for the winter 



sleep of Mammals, which are warmblooded; but the 



winter lethargy of the Adder illustrates the same 



general policy of evading danger by "lying low and 



saying nothing." In their winter retreats, in a 



rabbit's hole, it may be, or in the middle of a heap of 



rubbish, large numbers are often huddled together. 



