AQUATIC INSECTS 



decayed stems of water-plantain, Alisma, and Hungerford 

 has published photographs which show them beautifully 

 defined upon cat-tail leaves. Each egg has a round cap at the 

 top from which filaments extend out upon the surface of the 

 leaf. Length of adult, one to one and a quarter inches. 



Backswimmers, Family Notonectidae. — The members of 

 this family are unique in their ability to swim on their backs, 

 which are shaped like the bottom of a boat (PI. X). Their 

 long hind legs are used' like oars. 



Fig. i8o. — Backswimmer, Notonecta undulata, 

 with hind tip of its body thrust through water sur- 

 face for air. 



Backswimmer, Notonecta imdulata. — There are several 

 species of backswimmers all of which hang head-downward 

 from the surface with their long hind legs extended like oars 

 and the ends of their bodies thrust up to the air (Fig. i8o). 

 When disturbed they dive to the bottom, carrying a silver 

 film of air on the ventral side of the body, and remain sub- 

 merged, anchored by their front feet to a plant stem. They 

 are extremely active, with strong grasping fore-legs and a 

 beak with which they can inflict a burning sting, the effect 

 of which may last for some time in persons susceptible to 

 poisons. Although they are themselves predacious, their 

 young are preyed upon by nearly every other carnivorous in- 

 sect including adults of their own kind. They produce many 

 young; Hungerford found 252 mature eggs in Notonecta 

 irrorata. In that species egg-laying goes on from Alarch to 

 June and the adults live at least a year. Notonecta undtdata 

 (Fig. 180) is the commonest backswimmer, and is generally 



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