30 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 85 



insects so fragile, so highly organized, with a host of powerful 

 enemies, but themselves destitute of means of attack or defense, 

 should contrive to exist at all, is remarkable." Doctor Sharp here 

 falls into the same error the selectionists often do, namely, of taking 

 the struggle for existence too seriously. While mayflies are a favorite 

 food of many predators, the evidence does not indicate that they are 

 eaten out of proportion to their numbers. They are also very fecund, 

 practically the whole body content of a female mayfly consisting of 

 the two egg masses. The annual occurrence of swarms covering the 

 foliage along streams (dating back as far as such things were re- 

 corded) is proof enough that enemies do not permanently reduce the 

 numbers of mayflies, and furthermore that the so-called defenses or 

 protective adaptations, of which mayflies are so nearly destitute, are 

 not essential to the maintenance of species in large, even overwhelm- 

 ing numbers. 



PLECOPTERA (STONEFLIES) 



Protective adaptations. — The stoneflies are mostly plainly colored 

 but some are rather bright yellow ; they are poor fliers but some of 

 them are said to emit a liquid from the basal articulations of the legs, 

 a performance usually classed as protective. The nymphs are aquatic 

 in habit, good swimmers, and obscure in color. 



Bird enemies. — Stoneflies have been identified in the stomachs of 

 41 species of nearctic birds, usually in no very large numbers. The 

 total number of identifications is 80 ; the percentage of identifications 

 among those of all insects, .0419; and the percentage of species in 

 this order among those of all insect species known, .0780. 



Other enemies. — Dragonfly nymphs prey upon those of stoneflies, 

 and a few fishes, salamanders, frogs, and turtles feed upon these 

 insects, either in the immature or mature condition according to 

 availability. Needham says : " Hudson has demonstrated the im- 

 portance of stoneflies as fish food in the mountain streams of New 

 Zealand" (Fresh-water Biology, 1918, p. 884), and Muttkowski 

 reports that 90 per cent of the food of trout in Yellowstone National 

 Park consists of them. 



Discussion. — The Plecoptera are a small group of insects of re- 

 stricted habitat, one we should therefore not expect to find preyed 

 upon extensively. They are eaten by various enemies, however, more 

 or less in proportion to their abundance, and the evidence does not 

 seem to indicate that special defenses of any kind enter into the 

 equation. 



