Marine Insects 295 



air, as do their fresh-water relations, by means of 

 gill-filaments, or simply through the surface of the 

 skin. Many species of Beetles inhabit the shore, 

 and are submerged twice daily, when they lurk 

 under stones or burrow into the sand ; their hairy 

 bodies are not easily wetted, and in one of the 

 best known marine beetles (Aepus) there are paired 

 air-sacs in the hind-body which are believed to act 

 as reservoirs for breathing while the tide is up. 

 Several kinds of very small Springtails may be seen 

 on the surface of rock-pools at low-tide ; probably 

 when the water rises they retire into crevices of 

 the rocks. They are covered with a very fine, 

 dense pile, and it seems impossible to wet them. 

 The absence of wings is a common character among 

 sea-shore insects. The beetles of the genus Aepus 

 are wingless and so is the small bug Aepophilus 

 often found in their company, as well as the female 

 of the midge Clunio whose mate, though winged, 

 appears not to fly but to use his wings as sails as 

 he skims over the surface of the rock-pools. The 

 tendency of insects on oceanic isles to lose their 

 wings has often been noticed, and the loss of the power 

 of flight explained as an advantage, since insects 

 which do not fly cannot be blown out to sea. 

 Possibly the absence of wings in so many sea-shore 

 insects can be explained in like manner. Several 

 genera of pond-skaters have one or two species which 

 frequent the water of estuaries and harbours ; these 

 are in all cases wingless, though their fresh-water 

 relations, are, as a rule, winged. The extreme of 

 adaptation to marine life is shown by the bugs of 

 the genus Halobates (fig. 154) (171) — also belonging 

 to the family Hydrometridse — with their short anchor- 

 like fore-legs and their immensely long and slender 

 middle and hind-legs, the middle shin and foot being 



