11 



FLIES WITH AQUATIC LARV^ 



123 



popular name of Blood-worm.^ When of full size it 

 is nearly one inch long. These larvae protect them- 

 selves by making burrows out of 

 particles of earth or leaves, which 

 they weave together with the very 

 abundant secretion of the salivary 

 glands. When undisturbed, they 

 may often be seen to push the 

 head-end well out of the burrow 

 lor purposes of feeding ; at other 

 times the tail-end is pushed out 

 and waved to and fro in the water, 

 as a help to respiration. Now and 

 then they leave their burrows, and 

 swim through the water with a 

 lashing movement, twisting them- 

 selves into figures of eight. Occa- 

 sionally they rise to the surface, as 

 if to renew their supply of oxygen. 

 They are careless about finding 

 their way back to their burrows, for 

 in a short time they can glue to- 

 gether enough fresh fragments to 

 conceal themselves. The body of 

 the larva consists of a head and 

 twelve segments. The prothorax, 

 or segment next behind the head, 

 carries a pair of feet armed with 

 numerous hooks.. These are used for grappling. 



' Under this name are grouped the larva; of several species — 

 C. plumosus, dorsalis, &c. The specific distinctions, whether 

 of the larva or of the fly, are in most cases very minute. 



U 



Fig. 37. — Larva of Chiro- 

 nomu.s. Near the head 

 are .seen the rudiments 

 of the wings and legs of 

 the fly, enclosed within 

 the larval skin. 



