THE BIOLOGY OF PERLA IMMARGINATA SAY.* 



By Lucy Wright Smith. 



Introduction. Perhaps less is known concerning the Hfe- 

 histories and habits of the Plecoptera than of any other group 

 of aquatic insects. Hence a more extensive knowledge of stone- 

 flies along biological lines is desirable. At the suggestion of 

 Professor James G. Needham such a study was commenced 

 at Ithaca in the fall of 1910. 



This locality with its many creeks and spring brooks is 

 an excellent collecting ground for Plecoptera, and the equip- 

 ment of the limnological laboratory of Cornell University 

 makes an intensive study of aquatic forms possible. The 

 essential factor in rearing stone-flies, as in many other stream- 

 inhabiting insects, is running water. This is provided by a 

 series of taps in a roof garden aquarium and also in a small 

 artificial pond out of doors. 



Methods. With the hope of obtaining truer results by 

 keeping conditions as natural as possible, most of this study 

 is being carried on out-doors. Some care must be taken in 

 transporting stone-fly nymphs from the stream to permanent 

 quarters. Full grown nymphs can breathe air directly, and 

 have been carried most successfully wrapped in a wet cloth or 

 packed in damp moss. Smaller nymphs can be taken safely 

 for short distances in collecting jars full of clean, cold water. 



In the artificial pond the nymphs are kept, eight to ten 

 together, in cylindrical cages made of galvanized wire screen 

 with cheese cloth covers. For small nymphs it is necessary to 

 have the lower part of the cage lined with cloth. The cages 

 are partially submerged in the current near the taps. With 

 flat stones and bits of water weed in the bottom, and a steady 

 flow of water, the nymphs can live a natural life. 



The shyness of adult stone-flies makes field observations at 

 close range impossible. Consequently they are kept in screen 

 cages of about two by three feet. Here again an imitation of 

 natural environment is attempted. This is done by keeping 

 green twigs, clumps of sod, stones and pans of water in the 

 cages. 



*Contribution from the Limnological Laboratory of Cornell University. 



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