104 A NATURALIST IN THE GREAT LAKES REGION 



be found than those enabling the land animals to live in the 

 water. Insects likely evolved from land forms and never did 

 live in the water until some of them took to it as a secondary 

 consideration. They are primarily air breathers, taking the 

 air in through numerous spiracles on the sides- of the body to a 

 system of internal, ramifying air tubes. When they took to the 

 water they were forced to strange devices. Some diving beetles 

 like Dytiscus and some of the Hemiptera like the giant water 

 bug carry down a supply of air between the concave back of the 

 abdominal portion and the overlying convex wing covers. The 

 spiracles or breathing pores, which on most insects are on the 

 sides of the abdomen, are now on its top, which is the bottom of 

 the air chamber. Other animals enmesh enough air in the hairs 

 of body and legs to last them awhile; they seem to carry a film 

 of silver over the parts, the air film reflects so much light. The 

 common water scorpion has a long air tube at the posterior end 

 of the body so it can stand submerged on some aquatic plant and 

 still breathe through its air tube, the open tip of which is kept 

 at the surface (Fig. 212). 



Even the spiders have taken to the water. Some common 

 locally walk on the water and count it no miracle, they even run 

 with celerity, capturing flies and gnats out of the reach of their less 

 fortunate kind. One, the diving spider, hunts under water, even 

 spins its silken nest below the surface. This nest is cup shaped, the 

 opening down, and the adult spider carries down to the eggs and 

 young a supply of air enmeshed in the hair of abdomen and legs 

 that it scrapes off so as to keep the cup full until the young are 

 old enough to come to the surface for their own supply (Fig. 213). 



Some insect larvae are also air breathers and must come to 

 the surface to renew their supply. Such, fortunately for us, are 

 the mosquito larvae that we may exterminate by oiling the ponds 

 and ditches where they breed, so they cannot get to the top. 

 Such, as also the adult insects already described, are really air 

 breathers. But there is a host of insect larvae that are true 

 water breathers, taking in the oxygen by means of gills. These 



