318 A BOOK OF INSECTS 



(Collembola) disport themselves on the surface of the 

 water, both fresh and salt, and that at least one species 

 can remain submerged for weeks together. The most 

 remarkable of all water - frequenting insects, however, 

 are found among the Hymenoptera. One ichneumon 

 (Agriotypus armatus) goes under water, and remains 

 there for a considerable period, in order to lay her eggs 

 in caddis-worms. The parasite larva lives inside the case 

 of its host, and ultimately spins its cocoon there. In 

 what manner its respiration is effected remains a mystery. 

 Further, in the Proctotrypid sub-family Mymarince (the 

 members are sometimes called " fairy-flies " on account of 

 their extreme daintiness and minuteness) we have a little 

 group of species which enter the water and lay their 

 eggs within the eggs of aquatic insects. Most of them 

 employ their legs for swimming, but at least one species 

 {Caraphractus ductus — often termed Polynema natans) 

 actually uses its wings. It flies under water ! This insect 

 was first observed, in 1863, by Lord Avebury ; but its 

 life-history has more recently been investigated by Mr. 

 Fred Enock. The eggs are believed to be laid in those 

 of a dragon-fly. According to Sir Ray Lankester, these 

 minute egg- wasps have no tracheal system, but the 

 manner in which their tissues are aerated is apparently 

 unknown. 



