AQUAT C INSECTS 



911 



in the scum and about the edges of all sorts of fresh water, 

 while their adults swarm in thickets about the shores of pools. The 

 Ptychopteridae inhabit swales, their larvae living in the rotting trash 

 at the edge of the water, and the adults fluttering about the tops 

 of the adjacent herbage. The dixa midges (Dixidae) inhabit spring 

 brooks and clear pools, and their larvae (Fig. 1379), with bodies 

 bent double, slide out upon the surfaces 

 of wet leaves and stones, or edge off into 

 the water and whirl about in short curves ; 

 the adults dance in companies above the 

 surface of the water. Some larvae of the 

 Rhyphidae likewise inhabit pools, and the 

 adults sometimes assemble and dance in 

 the shelter of forest trees at some dis- 

 tance from the water. The few known 

 aquatic members of the Leptidae live as 

 larvae in streams and cling with the well- 

 developed claws of their stout muscular 

 abdominal prolegs to the surfaces of 

 stones; the adults flit about the shore, FiG.i, 179 . Larva m and P u pa (S) of 



j i ,| . 11 i | the dixa-midge. (After Tohannsen.) 



displaying their unusually gaudy colors 



and velvety textures. These are small and comparatively un- 

 important families. 



Then there are a few large families of which but a small proportion 

 of the members are adapted to aquatic life. The crane-flies (Tipu- 

 lidae) are essentially terrestrial: most of them live in moist earth or 

 wet leaves. Some are strictly amphibious, like Epiphragma (Figs. 

 1380 and 1381). They possess as larvae the usual terminal spira- 

 cles for breathing air, but have these set upon a respiratory disc 

 that can be closed by folding together on the middle line, and they 

 have a bundle of four anal gills that may then be protruded for 

 use under water. There is a fine development of fringes about the 

 respiratory disc of other species, and these fringes spread out upon 

 the surface film, holding the spiracles up to the air, while the larvae 

 are moving about in the water below. A few only of the syrphus 

 flies (Syrphidae) are aquatic, but the larvae of certain of these, the 

 common "rat-tailed maggots" are most peculiar and interest- 



