PLECOPTERA NYMPHS OF NORTH AMERICA 5) 
Mae iene ooley: GC. kk. Crosby; Y. T. Chu; G..S. Dodds: T..H. 
Frison; J. G. Greeley; W. A. Howard; O. A. Johannsen; P. Ken- 
nedy; Elsie B. Klots; M. D. Leonard; R. Muttkowsky; J. G. 
Needham; P. R. Needham; Sid Robinson; Theressa R. Seeman ; 
C. K. Sibley; R. J. Weith; C. F. Wu. 
DISTRIBUTION AND HABITAT 
So far as is known, stoneflies are world wide in their distribu- 
tion, and may be found wherever suitable water for their develop- 
ment occurs. Of the two hundred eleven known North American 
species, the greater number are found in the Eastern States, the 
Rocky Mountain area, and in the far Western States, wherever 
cold, fresh-water streams exist. However, stoneflies also occur in 
places where the streams are usually sluggish and where the water 
becomes quite warm. Thus there have been recorded fourteen spe- 
cies from Kansas and twenty-four species from Ilinois. 
The nymphs of Plecoptera may be collected at any time of the 
year. Some species normally inhabit the very small, cold, upland 
spring brooks, while others are to be found only in the big swift- 
water streams, especially in those with stony beds. There may be 
decided differences in the physical character of streams which the 
various species require, but, foremost of all, they must have 
reasonably pure and well-aerated waters. 
Most of the stoneflies are very sensitive to polluting substances, 
and the absence of nymphs in permanent fresh-water streams 
often is an indication of some type of pollution. Any substance 
which possesses toxic properties, or any organic material which in 
its oxidation process reduces the oxygen content of the water, 
may kill the entire stonefly fauna before the water becomes un- 
bearable to much of the other aquatic life. Whereas it is not safe 
to assume that fresh water streams in which stoneflies are absent 
are necessarily polluted, it is always safe to assume that, wherever 
they are present, the waters are relatively clean. 
The greater majority of nymphs are found in running water ; 
some species inhabit lakes and ponds also, but only when the 
ponds are part of a stream which continually brings in a fresh 
water supply, and usually only near the lake shores where the 
water is kept in motion. 
FOOD HABITS 
In the earlier literature on Plecoptera we usually find that 
stonefly nymphs ‘‘are carnivorous,’’ and that the adults ‘‘do not 
take food.’’ Even in some of the more recent textbooks on en- 
