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 

 Gar way 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 wOiich 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 

 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 



