206 Annals Entomological Society of America [Vol. VI, 



adaptations for clinging, running and swimming niake their ex- 

 istence fairly easy, especially in this stream where the crayfish 

 is the only enemy of any account. 



Food Habits. The long standing supposition that stone-fly 

 nymphs devour their weaker neighbors, has been confirmed for 

 this species in a study of their food habits. This has been done 

 by examining the stomach content of nymphs taken from the 

 stream, and also by feeding those in captivity. Dissections of 

 mature nymphs show the alimentary canals empty and in many 

 cases even so collapsed that they are difficult to find at all. 

 Likewise the nymphs kept for rearing refused all food for eight 

 or ten days before transformation. 



With growing nymphs it is different; here it is a task to supply 

 them with enough food to prevent their eating one another. 

 In a single day three or four of these nymphs will dispose of a 

 score or more black-fly larvae and half as many small may-fly 

 nymphs. Their greed is brought out even more strikingly by 

 examining the food mounts of nymphs taken from the' stream ; 

 whole specimens of midge larvae are found not uncommonly 

 and sometimes a may-fly nymph with even the gills intact. 

 The mass of food, however, consists of innumerable shapeless 

 scraps of chitin with scattered fragments of abdomens, setae, 

 antennae, legs; or claws, whole heads, mandibles, maxillae, and 

 labia, making possible the recognition of may-fly and stone-fly 

 nymphs, midge and simulium larvae and pupae. 



The only evidence of any herbivorous tendency in this 

 species is the presence of an immense number of diatoms in 

 food amounts. Of course this is a question of direct or indirect 

 eating. One would expect to find diatoms in a food mount 

 made up of pieces of may-fly nymphs and chironomid larvae, 

 and the natural supposition might be that the stone-fly got 

 them second hand. Yet such a statement cannot be made 

 without some hesitation, because the number of diatoms in the 

 mounts seems to increase with a general decrease in the amount 

 of food; and also because diatoms have been found to be the 

 chief food of some of the smaller species of stone-flies. 



Transformation. Just before the time of transformation 

 when the nymphs cease eating they become sluggish. And as 

 the time approaches they crawl further and further toward 

 the surface of the water, and flnally entirely out of it where 

 they often remain for hours before emergence. The actual 



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