204 BRITISH SERPENTS. 
especially the mice and slow-worms on the hillsides, 
and the water-voles at the river-side. These three are 
their staple articles of diet here. The bracken on 
Garway Hill, which covers a very large area, swarms 
with mice, which are also of course plentiful in the 
woods, while the slow-worm is perhaps more abun- 
dant across the river. The slopes of this hill are hot 
and dry and face the south—conditions which we saw 
were all characteristic of the taste of adders; so that 
altogether everything is in the adder’s favour in the 
Monnow Valley. But there remains the problem of 
the entire absence of the ring snake. Without going 
over the same ground again, it is quite obvious that it 
is precisely because the conditions are so favourable 
to the adder that the ring snake is not equally at- 
tracted. In particular, the nature of the ground and 
the food-supply are not suited to its requirements. 
There are no small streams, few ponds, and therefore 
comparatively few frogs, the favourite food of the 
ho] 
ring snake. Heaps of garden rubbish and manure 
are few and far between, and the slopes of the hill- 
sides too exposed in winter for the eggs to survive 
if not hatched out in the autumn. The conditions 
favouring the ring snake are better found on the 
southern slopes of The Graig some miles away, and 
accordingly there Tropidonotus natrix flourishes. It 
was suggested to me by a naturalist that possibly the 
adder had exterminated the ring snake here, but I 
have not been able to obtain any evidence to support 
