288 THE BIOLOGY OF INSECTS 



and others have pointed out how many of the insects on 

 oceanic islands are flightless, and suggested that this 

 condition may be regarded as advantageous, as flying insects 

 in such localities would be in continual danger of being 

 blown out to sea. It is possible also that life close to the 

 sea-shore of continental tracts and islands is safer for insects 

 that fly infrequently or not at all. Returning to the flies 

 of our own coasts, it is interesting to find among the pre- 

 daceous Empidae — a family belonging to a section of the 

 Diptera far removed from Coelopa and its allies — the little 

 sand-haunting Chersodroniia arenaria, which shows the 

 same small head and flattened body-form as these, and has 

 its wings not only narrow and pointed but so shortened as 

 to be useless for flight. 



Perhaps the most characteristic and specialised of all 

 shore-haunting Diptera are some minute midges of the 

 family Chironomidae, the adaptation of whose larvae for 

 aquatic life has already been mentioned (p. 45). Chiro- 

 nomid larva have been dredged off the European and 

 American coasts at depths of 15 and 20 fathoms, and one 

 of these was described as a marine annelid by a naturalist 

 who failed to recognise it as an insect grub. Several species 

 of Chironomus and alUed genera haunt the rocks exposed 

 at low tide, and the more remarkable of these show the 

 tendency of marine flies already mentioned towards loss of 

 wings. In Eretmoptera browni, described by V. L. Kellogg 

 (1900) from the coast of California, the wings in both sexes 

 are " narrow and strap-like and wholly without veins, not 

 specially thin or delicate but rather thickened." A struc- 

 tural feature of much interest, suggesting the primitive 

 standing of the insect, despite its adaptation for marine 

 life, is that the hindwings instead of being the stalked, 

 knob-like '' balancers " usual among the Diptera, '' are 

 minute scale-like processes, appearing like rudiments of 

 wings " of the ordinary type. *' The flies," remarks 

 Kellogg, " of which there were very many, were resting and 

 running on the surface of the ocean water of tide-pools 

 and had a tendency to gather in large numbers in patches 



