CHAPTER IV 

 ADAPTATIONS OF AQUATIC INSECTS 



Ease, versatility and perfection of adaptation are beautifully exem- 

 >lified in aquatic insects. 



Systematic Position. Aquatic insects do not form a separate group 

 in the system of classification, but are distributed among several orders, 

 >f which Plecoptera, Ephemerida, Odonata and Trichoptera are pre- 

 eminently aquatic. One third of the families of Heteroptera and less 

 than one fourth those of Diptera are more or less aquatic. One tenth 

 >f the families of Coleoptera frequent the water at one stage or another, 

 two families of Neuroptera, and only half a dozen genera of Lepidoptera. 

 A few Collembola live upon the surface of water; and several Hymenop- 

 tera, though not strictly aquatic, are- known to parasitize the eggs and 

 larvae of aquatic insects. 



The change from the terrestrial to the aquatic habit has been a 

 gradual change of adaptation, not an abrupt one. Thus at present there 

 are some tipulid larvae that inhabit comparatively dry soil; others live 

 in earth that is moist; many require a saturated soil near a body of 

 water and many, at length, are strictly aquatic Among beetles, also, 

 similar transitional stages are to be found. 



Food. Insects have become adapted to utilize with remarkable 

 success the immense and varied supply of food that the water affords. 

 Hosts of them attack such parts of plants as project above the surface of 

 the water, and the caterpillar of Paraponyx (Fig. 174) feeds on sub- 

 merged leaves, especially of Vallisneria, being in this respect almost 

 unique among Lepidoptera. Hydrophilid beetles and many other 

 aquatic insects devour submerged vegetation. The larvae of the chry- 

 somelid genus Donacia find both nourishment and air in the roots of 

 aquatic plants. Various Collembola subsist on floating algae, and larvae 

 of mosquitoes and black-flies on microscopic organisms near the surface, 

 while larvae of midges, Chironomus, find food in the sediment that accu- 

 mulates at the bottom of a body of water. 



Predaceous species abound in the water. The backswimmer, 

 Notonecta (Fig. 227) approaches its prey from beneath, clasps it with 

 the front pair of legs. and pierces it. The water scorpions, Nepa and 



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