228 Aquatic Organisms 



larvae are the well known "wrigglers" that live in rain 

 water barrels and in temporary pools. They are 

 readily distinguished from other Dipterous larvae by 

 their swollen thoracic segments and their tail fin. The 

 pupae are free swimming and hang suspended at the 

 surface with a pair of large respiratory horns or trum- 

 pets in contact with the surface when at rest. 



FIG. 136. A few of the component egg-strings, magnified. 



The larvas of the horseflies are burrowers in the mud 

 of the bottom. They are cylindric in form, tapering 

 to both ends, headless, appendageless, hairless, and 

 have the translucent and very mobile body ringed with 

 segment ally arranged tubercles. They are carnivorous, 

 and feed upon the body fluids of snails and aquatic 

 worms and other animals. The white spiny pupae are 



