ESSEX REPTILES AND AMPHIBIANS. 147
panion; but, one morning, I found that the vole had killed the
viper and eaten the head and an inch or so of the body. Very
likely lizards form a large part of vipers' food; and we noticed
that the common lizard was remarkably numerous in the Forest
in 1919.
2.—THE GRASS SNAKE OR RING SNAKE
(Tropidonatus natrix).
is common in most if not all parts of Essex, and is really abun-
dant at Theydon Bois. In a quarter of a mile, near the lake at
Birch Hall, it is not unusual to see ten or a dozen snakes. They
are, as a rule, very timid, and retreat beneath the dense thorny
thickets, or project themselves like water voles into the lake.
Nevertheless, we have sometimes managed to bag three or four
in half an hour.
In Essex, the grass snake is very fond of water. Several
times I have seen snakes swimming spontaneously across the
widest part of a lake; sometimes the head and three inches
of the body are held above the water, but at times they swim
with the tip of the nose and the eyes only above the surface.
It is, too, not uncommon to see snakes entirely submerged, and
sometimes a yard deep, exploring the recesses of a pond. While
thus engaged the reptile looks like an eel, and must frequently
be mistaken for the fish.
Repeated diving soon tires a snake, and if pursued in a boat
the animal is utterly exhausted after about a dozen dives; and
so, too, is the rower, for the snake is extremely agile, and dodges
about while under water. It is strange that the snake does not
seek to escape by swimming to the cover of the bank without
rising to the surface—a feat it is quite capable of doing, for I
have watched snakes, when not alarmed, swimming for some
minutes beneath the surface of a pond.
In spite of many authors, grass snakes eat toads; and, per-
haps, these form their chief food in Essex. I have often forced
a bulky snake to disgorge its prey, and, at Theydon Bois, a toad
has been the result in every instance. I have never seen a grass
snake either in the early morning or in the late afternoon or
evening, although I had excellent opportunities for daily obser-
vations at Birch Hall.