f 



Among aquatic insects, niinute slender dipterous larva^, belonging mostly 

 to Chironoraus, Corethra, and allied genera, are of remarkable imixjrtance, 

 making, in fact, nearly one-tenth of the food of all the fishes studied. 

 They are most abundant in Phenacobius and Etheostoma, which genera, 

 have be come especially adapted to the search for these insect forms in shallow 

 rocky streams. Next I found them most generally in the pirate perch, 

 the brook silversides, and the stickleback, in which they averaged forty- 

 five per cent. They amounted to abou^ one third the food of fishes as 

 large and important as the red horse and the river carp, and made nearly 

 one-fourth that of fifty-one buffalo fishes. They appear further in consid- 

 erable quantity in the food of a number of the minnow family fNotropis, 

 Pimephales, etc.), which habitually frequent the swift water of stony 

 streams, but were curiously deficient in the small collection of miller's 

 thumbs (Cottida^) which hunt for food in similar situations. The sun- 

 fishes eat but few of this important group, the average of the family be- 

 ing only six per cent. 



Larvae of aquatic beetles, notwithstanding the abundance of some of the 

 forms, occurred in only insignificant ratios, but were taken by fifty-six 

 specimens, belonging to nineteen of the species, — more frequently by the 

 sunflshes than by any other group. The kinds most commonly captured 

 were larvae of Gyrinida? and Hydrophilidte : whereas the adult surface 

 beetles themselves (Gyrinus, Dineutes, etc.)— whose zigzag-darting swarms 

 no one can have failed to notice— were not once encountered in my studies. 



The almost equally well-known slender water-skippers (Hygretrechus) 

 seem also completely protected by their habits and activity from capture 

 by fishes, only a single specimen occurring in the food of all my specimens. 

 Indeed, the true water bugs (Hemiptera) were generally rare, with the ex- 

 ception of the small soft-bodied genus, Corisa, which was taken by one 

 hundred and ten specimens, belonging to twenty-seven species, — most 

 abundantly by the sunfishes and top minnows. 



From the order Neuroptera, fishes draw a larger part of their food than 

 from any other single group. In fact, nearly a fifth of the entire amount 

 of food consumed by all the adult fishes examined by me consisted of 

 aquatic larv« of this order, the greater part of them larvje of day files 

 (Ephemeridte), principally of the genus Hexagenia.* These neuropterous 

 larva? were eaten especially by the miller's thumb, the sheepshead, the 

 white and striped bass, the common perch, thirteen species of the dartere, 

 both the black bass, seven of the sunfishes, the rock bass and the croppies, 

 the pirate perch, the brook silversides, the sticklebacks, the mud minnow, 

 the top minnows, the gizzard shad, the toothed herring, twelve species 

 each of the true minnow family and of the suckers and buffalo, five cat- 

 fishes, the dog-fish, and the shovel fish, — seventy species out of the eighty- 

 seven which I have studied. 



Among the above, I found them the most important food of the white 

 bass, the toothed herring, the shovel fish (fifty-one per cent ), and the 

 croppies; while they made a fourth or more of the alimentary contents of 

 ths sheepshead (forty-six per cent.), the darters, the pirate perch, the com- 

 mon sunfishes (Lepomis and Chaniobyttus). the rock bass, the little pick- 

 erel, and the common sucker (thirty-six per cent.). 



Ephemerid larva* were eaten by two hundred and thirteen specimens of 

 forty-eight species — not counting young. The larva^ of Hexagenia. one of 

 the commonest of the "river flies," was by far the most important insect 

 of this group, this alone amounting to about half of all tlie Nouroptera 

 eaten. They made nearly one half of the food of the sliovel fish, more 

 than one tenth that of the sunfishes. and the principal food resource of 

 half-grown sheepshc^ad : but were rarely taken l)y the sucker family, and 

 made only five per cent, of the food ot" the catrtsli group. 



The various larva^, of the dragon flies, on the other hand, were much 

 less frequently encountered. They seemed to be most abundant in the food 

 of the grass pickerel, (twenty-five per cent.), and next to that, in the crop- 

 pie, tlie pirate perch, and the common perch (ten to thirteen percent.). 



* The winged adults of this and related genera are often called " river flies " in Illinois. 



