178 THE ENTOMOLOGIST. 



the stream itself, though occasionally straying on to stagnant 

 water, where are found the other species of Gerris, Hydrometra, 

 &c. In fairly clear ponds Notonecta, Ilyocoris (Naucoris), and 

 Corixa can he seen swimming helow, and at times ascending to 

 the surface for air, hut as a rule one has to trust to a thorough 

 "sweeping" of the water for these insects. In sweeping a very 

 weedy pond (especially one infested with the Canadian pond 

 weed, Elodea canadensis, formerly called Anacharis canadensis), 

 the contents of the net should he turned out upon a piece of 

 white mackintosh (or similar suhstance). The weed should then 

 he shaken and discerpted piece hy piece in some water in a small 

 portable white-bottomed dish, a number of small bugs (Plea, 

 Micronecta, &c.) being thus taken, which might otherwise escape 

 notice from being concealed in a mass of weeds, or imprisoned 

 between two or more leaves which have adhered in consequence 

 of the removal of the plant from the pond. 



Nepa and Ranatra watch for their prey resting on the bottom 

 of the pond, concealed in mud ; the collector should therefore 

 place the net close to a large plant or mass of smaller plants, 

 about an inch beneath the surface of the mud, and with a swift 

 twisting movement draw it to the surface. The net should then 

 be filled with water and shaken, the water filtering through the 

 meshes and carrying with it the finer particles of mud. When 

 this has been repeated several times, most of the mud will have 

 escaped, and the contents of the net will now be ready for 

 examination. 



Waterbugs may be searched for in swift running streams and 

 in small stagnant ponds, while one or two species of Corixa are 

 scarcely fouud elsewhere than in brackish dykes near the sea ; 

 small ponds, however, harbouring but few weeds, and with a 

 perpetual bottom of decaying oak, elm, or beech leaves, I have 

 not found productive. It is in these places that the crustacean 

 Asellus is to be found in "herds," and I always accept their 

 presence in large quantities as an indication of the absence of 

 waterbugs. Moreover, the latter are unlikely to occur in ponds 

 infested with frogspawn, and their condition upon extraction 

 from a mass of weeds and watersnails, enveloped in the spawn, 

 is not very satisfactory. 



One small species, A'epophilus bonnairii (whose exact systematic 

 position is doubtful), has been discovered at various seaside 

 localities in England and Ireland (but not, I think, in Scotland) 

 under stones and in fissures of rock not far above low water. 



As a rule, waterbugs have a wide distribution. Some species 

 of Gerris and Corixa, however, are found only in the elevated 

 portions of Scotland, though occasional stragglers occur in the 

 south ; one species — Corixa caledonica (cognata) — is known to 

 science only from Scotland, though distributed there from Loch 



