FIELD BOOK OF PONDS AND STREAMS 



Occurrence. — Quebec and south; common southward, New 

 York, Rhinebeck. 



Fig. 202. — I, A caterpillar of rapid waters, Elo- 

 pJiila fulicalis (after Lloyd); 2, pupal case (after 

 Lloyd); 3, the moth. 



Although most aquatic caterpillars live in quiet waters, 

 there is at least one, Elophila fulicalis (Fig. 202, i), which is 

 at home in the rapid streams where mayflies and stoneflies 

 abound. There it lives on water-washed rocks, breathing by 

 means of the unbranched tracheal gills which extend in double 

 rows along each side of its body. 



It weaves a silken canopy above itself, cementing the irreg- 

 ular edges to the rock except in two or three places. These 

 openings allow the water to circulate freely beneath the cur- 

 tain. Canopies made by young larA^ae are only half an inch 

 long but those of the fullgrown larvae measure four or five 

 inches long and are an inch wide. The caterpillars feed 

 upon the algal ooze covering the rock beneath them, the 

 abundant Scenedesmus and the beautiful green spheres of 

 Pediastrum. 



Shortly before it is ready to pupate the fullgrown larva 



260 



