188 



ENTOMOLOGY 



FIG. 229. 



has some means of keeping its body dry. This is accom- 

 plished usually by hairs, set together so thickly that water 



cannot penetrate between them. 

 As the legs and body of G err is 

 are rendered water-proof by a vel- 

 vety clothing of hairs, the insect, 

 though heavier than water, is able 

 to skate about on the surface. 

 Gyriwus, by means of a similar 

 adaptation, can circle about on the 

 surface film, and minute collem- 

 bolans leap about on the surface as 

 readily as on land. 



The modifications of the legs 

 for swimming have often impaired 

 their usefulness for walking, so 

 that many aquatic Coleoptera and 

 Hemiptera can move but awk- 

 wardly on land. When walking, 

 it is interesting to note, Cybister 

 and some other aquatic forms no 

 longer move their, hind legs simul- 

 taneously as they do in swimming, 

 but use them alternately, like ter- 

 restrial species. 



The adaptations for swimming 

 do not necessarily affect the power 

 of flight. Dytiscus, Hydrophilus, 

 Gyrinus, Notonecta, Benacus and 

 many other Coleoptera and Hemip- 

 tera leave the water at night and 

 fly around, often being found about 

 electric lights. 



Respiration. Aquatic insects have not only retained the 

 primitive, or open (holopneustic) , type of respiration, charac- 



Larva (A) and pupa (5) of 

 mosquito, Culex pipiens. r, respi- 

 ratory tube; t, tracheal gills. 



