o6 



ANIMAL COMMUNITIES OF STREAMS 



May-fly nymphs, the flattened Heptageninae, and the very awkward 

 damselfly nymph, Argia, evidently succeeding well together. This 

 fact makes the value of the flattening as an adaptation appear nil. 

 There are also the larvae of midges (Chironomus sp.) (98) and of horse- 

 flies (Tab anus) (Figs. 51, 52). The adults of the latter deposit their 

 eggs in great masses on the tops of the stones which protrude from the 

 water. The stone-fly nymphs, similar to the Heptageninae May-fly 



Representative Aquatic Insects of a Rapids Community 



Fig. 39. — The net of the brook caddis- worm {Hydro psyche) seen from the front. 

 Drawn from a specimen which made its case against the side of an aquarium (original). 



Fig. 40. — The same in its case with the net adjoining the opening which faces 

 upstream (original). 



Fig. 41. — The larva of a caddis-fly (Helico psyche) with a case made from pebbles, 

 in the form of a spiral; 2\ times natural size (original). 



Figs. 42, 43. — The water-penny larva of the brook beetle (Parnidae) seen from 

 above and below (43); 2§ times natural size (original). 



nymphs in form and appearance, are found here also. Perhaps the 

 most bizarre of all are the water-pennies. These are round flat objects 

 adhering to the under sides of stones, and not looking like animals at 

 all. They are the larvae of a parnid beetle (Psephenus). Figs. 42 and 

 43 show two views of a larva. The old larval back becomes the cover 

 for the pupa. The adults live under the stones also and their general 

 appearance is like that of the parnid in Fig. 47. Sessile or attached 

 animals are common in the brooks, but their numbers vary greatly from 



