AQUATIC INSECTS IN NEW YORK STATE 209* 



on the bottom in the midst of a very thin hiyer of silt and veg- 

 etable debris covering the white sand. Its loose gelatinous case 

 is covered with adherent silt, and takes on the general, protec- 

 tive color of the bottom. As is well known, the larvae of the 

 larger red species are among the most characteristic bottom 

 forms in all our larger and deeper lakes, being usually asso- 

 ciated with deep water mollusks (Pisidium) and caddis fly 

 larvae. This distribution, the natural abundance of the larvae^ 

 and the constant succession of generations through the year, 

 leaving no period of absence of the larvae from the water, con- 

 stitute the claim of these larvae to economic importance. 



The pupae at first are red, but that color is generally quickly 

 obscured by the development of the pigment of the adult insect. 

 Within a few days at most after the transformation from the 

 larva, the pupa rises to the surface and floats there, descending: 

 when disturbed, but quickly rising again. Pupae are less uni- 

 formly distributed over the surface than are larvae over the 

 bottom, for the wind may drive them together in great masses. 

 Pupae are often taken in numbers in a surface net in towing; 

 larvae are rarely taken so, and then only at night, and in shal- 

 low water, for the larvae often leave their retreats at night and 

 go swimming considerable distances with figure-of-eight loop- 

 ings of the body. 



It will be seen in the table that, with the exception of trout 11,. 

 every trout that had eaten Chironomus at all had eaten either 

 larvae or pupae largely in excess; a large number of one stage^ 

 few or none of the other. In the light of the differences in hab- 

 its of larvae and pupae just stated, this should indicate that 

 some of the fish had been feeding chiefiy or wholly at the bot- 

 tom, others at the surface of the pond. The larger number of 

 larvae eaten may indicate either that larvae were more easily 

 obtained, or that they were preferred, or that bottom feeding 

 was j)ref erred. 



2 Corethra 



This is another form that is common in our northern lakes 

 generally. It was not studied at Bone pond, and was collected 

 there only b^' the trout. Corethra plumicornis is. 



