AQUATIC COLEOPTERA OF THE OUTER HEBRIDES 15 



under 400 ft. The central portion is almost level, and forms 

 an unbroken peat-bog over which are scattered scores of 

 lakes. In the southern region towards Loch Erisort they 

 are so numerous that the island consists of almost equal 

 portions of land and water." ^ 



There is, therefore, no scarcity of ground for collecting 

 aquatic insects ; but small bog-pools, although not scarce, are 

 not so abundant as in many peaty districts, the peat in most 

 parts of the northern district being exceedingly porous, owing 

 to the innumerable drainage channels which have been worn 

 in it by the winter rains. So efficient are these drainage 

 channels that a spate on even the largest rivers runs out in 

 less than two days, and, although many pools are to be 

 found immediately after some hours' rain, these very rapidly 

 disappear. 



A number of permanent pools are to be found along the 

 sides of the roads, and these are holes which have been dug 

 in the boulder or glacial clays to supply ballast for the roads. 

 These holes are to be found in all stages of evolution, from a 

 newly dug weedless pool to a typical Sphagnum pool, and I 

 spent a part of my time both in the north and in the south 

 of the island in studying the changes in the water-beetle 

 fauna of these ballast-holes as they evolved. 



The Tarbert district differs entirely from the northern 

 district in that it is altogether divided into mountain and 

 valley. On the mountains the peat is mostly very thin, and 

 the bare rock is freely exposed. There are here also a 

 number of lochs, mostly small, but there are also plenty of 

 pools quite apart from the ballast-holes along the roadsides. 



In both north and south I experienced the greatest 

 difficulty in adding species to my lists after the first two or 

 three days, because a few species occurred in almost every 

 place examined, while the rest turned up in ones and twos at 

 comparatively rare intervals. The difficulty was largel)- due 

 to the fact that there was very little variety of habitat. 



Apparently only three collectors have previously visited 

 the Outer Hebrides in search of beetles, and these all visited 



' F.J. Lewis, "The Plant Remains in the Scottish Peat Mosses," 

 part iii., Trans. Roy. Soc. Edin., xlvi., Part I. (No. 2), pp. 45, 46, 1908. 



