FIELD BOOK OF PONDS AND STREAMS 



Fig. 183. — Water boatman, Arctocorixa (Corixa) 

 alternata: i, nymph; 2, adult grasping a submerged 

 Chara stem, a characteristic pose. 



this species and by May 15 the total population was infested 

 with them. Length of adult, one quarter of an inch. 



Alderflies, Dobsons, Fish-flies, Spongilla-flies — Xeuroptera 



Members of only two families of the Nenroptera in our 

 fauna have aquatic larvse, the SialidcE, which contains the 

 alderflies, dobsons, and fish-flies, and the Sisyridce or Spon- 

 gilla-flies. 



Form and habits. — The adults have four wings and are 

 named Neiiroptera because of the many fine veins which run 

 through the wings. There is a complete change of form from 

 larva to adult, and the fullgrown larva always climbs out of 

 the stream to pupate. 



Occurrence. — The larvae of the Sialidce live in swift water, 

 where they hide under stones and are frequently found in 

 riffly shallows throughout the winter, but the Spongilla-fiies 



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