VERTICAL DlSTRIBUfrON OF RHOPALOCKKA IN THE ALPS. 323 



would afford the lesser elevations protection from the wind, would 

 cause the insects to be all blown off their treeless summits in no 

 time. Tlie paucity of species of Rhopalocera in the principal 

 mountainous districts in the British Isles supplies the direct 

 cause for their great scarcity at any considerable elevation; 

 1000 feet above the sea-level seems to be the highest vertical 

 limit beyond which the majority of species do not ascend in this 

 country. 



In the Alps all the circumstances are very different ; every- 

 thing, in fact, is favourable to the existence of Rhopalocera, the 

 absence of their pabula constituting the chief barrier to their 

 upper extension upon the mountains. Several species are ac- 

 cordingly known to exist even above the line of congelation, 

 among the snow, wherever small patches of vegetation can secure 

 a roothold among the rocks. Thus, upon the summit of the 

 Gornergrat, in the Pennine chain, at an elevation of over 

 10,000 ft., I have encountered one species, namely, Erebia 

 glacialis. Several odd specimens of the Vanessidse have been 

 seen at higher elevations still, but they are only wanderers to 

 those altitudes, and do not undergo their transformations there. 



The lower zones in the Alps of course contain the greatest 

 number of species, and the higher one ascends the fewer will they 

 become. 



One of the most familiar butterflies in the region in question 

 is the handsome Papilio podalirius, which is pretty plentiful in 

 most of the lower valleys, but does not attain to any great 

 elevation among the mountains, about 3800 ft. above the sea- 

 level being the highest altitude at which I have observed it. 

 P. machaon, which, however, is more local and generally less 

 common, ascends a few hundred feet higher, often occurring among 

 the pine woods of the lower alpine zone. The beautiful large 

 crimson-ringed Parnassius apollo is one of the most conspicuous 

 butterflies of the lower mountain region, and is also, on account 

 of its plentifulness, perhaps the most typical species in the Alps. 

 It occurs between the altitudes of 8000 and (5000 ft. I have found 

 it a little below the first-named figure at Stalden and Aigle in 

 the Rhone Valley, in the upper portion of the vine zone, but in 

 general it is not seen until this has been passed. Its upper limit 

 terminates amidst the forests of conifers. The closely allied P, 

 deliiis is much more local and scarce, and its area of distribution 

 is also considerably more circumscribed. Its lower limit slightly 

 overlaps that of the preceding species, but its upper limit extends 

 beyond the pine woods into the upper alpine region occupied by 

 the rhododendron and charming alpine plants, which give forth 

 such an array of bright-coloured flowers in the summer time, 

 affording abundant pleasure alike to the tourist and the scientific 

 traveller. This species sometimes reaches an altitude of close 

 upon HOOO ft., at which height I have seen it upon the Riffel Alp 

 near Zermatt. 



