ADAPTATIONS TO HAUNTS AND SEASONS 283 



freshwater insects it is natural to turn to a few examples 

 of the comparatively small number— probably, however, 

 amounting to hundreds of species — that haunt the margins 

 and tidal waters of the sea or venture themselves on its 

 surface. Insects are pre-eminently creatures of the air 

 and the land ; therefore we are surprised to notice the 

 wonderful modifications shown by many of them for life 

 in water, and the adaptation of others to marine conditions 

 is yet more surprising. Many of the marine insects, such 

 as aquatic beetles and bugs, and flies with submerged larvae, 

 with their near allies among freshwater groups, have passed 

 to sea through the brackish waters of estuaries or salt-marshes. 

 Others, belonging to groups that feed whether as adults 

 or larvae in decaying organic matter, seem to have been 

 attracted by the row of blackened seaweed that marks the 

 high-tide level along the coasts ; thence some have passed 

 on to find shelter and food in the varied animal and vegetable 

 substances along the tidal belt. Attention has already 

 been drawn in this chapter (p. 267) to the adaptability of 

 the Collembola (springtails) to very widely separated and 

 diverse haunts, largely owing to the comparative simplicity 

 of their structure. There are a number of springtails of 

 the Isotomine group to be found among the decaying wrack 

 flung up by the waves. Some of these belong to species 

 that live also inland, but some are known only from the 

 tidal margin though in widely separated parts of the world. 

 For example, Archisotoma heselsi (Fig. 70), a characteristic 

 member of the fauna of Spitsbergen, lives along the high- 

 tide mark of our British and Irish coasts as well as in 

 similar situations in Greenland, Tierra del Fuego, and 

 the sub-antarctic South Orkneys. Often very abundant 

 where found, this little insect appears to inhabit only the 

 tidal margins of the sea-coast in widely separated regions 

 of the globe. The most characteristic of shore-haunting 

 springtails is Anurida maritimay found in vast numbers 

 along the rocky coasts of our islands, of France, Heligoland, 

 and North America. Its form and habits have been 

 described in detail by A. D. Imms (1906). It is one of 



