THE HISTORY OF THE DOBSON. 43 



At long intervals the dobsons moult. Apparently they only 

 shed their skins about six times during the three years of their 

 existence in the water. Except for their increase in size there 

 is little change in their general appearance during this period. 



I am sure many boys will recognize the picture of the full- 

 grown dobson larva shown in Fig. 42. These larvse are also 

 often called " crawlers " by fishermen. They are frequently 

 used for bait in fishing. As will be seen, the head is large and 

 broad, and is provided with a pair of formidable jaws. There 

 are six long, strong legs on the three rings of the body just 

 behind the head. On each of the hinder rings of the body 

 is a pair of tube-like threads, by means of which the insect 

 breathes the air in the water. 



The dobsons prefer to live in the rapids of rivers and creeks, 

 where the water courses swiftly over the rocks. They ma}'- 

 often be caught by disturbing loose stones in such streams, 

 having some one else hold a net below so that the dobsons will 

 be carried into it by the rapid current. 



