272 BULLETIN OF THE BUREAU OF FISHERIES. 
Juty 13.—The species collected yesterday is much more abundant to-day. They swarmed all 
over me while I wason the dam. Every shaded place was covered with them. 
Juty 14.—Took photographs [see Pl. LXX, fig. 1] at about 5.30 a. m. of the gauge house on the 
dam between gates 29 and 30, covered with mayflies of which I collected specimens yesterday. In the 
lake above the dam there is a mass of cast skins, irregularly distributed, though the adults are distrib- 
uted along the dam very generally. Have not seen this species mating. 
From Keokuk to Montrose, Iowa, along the railroad track, the air was full of mayflies, all apparently 
the same species. The same conditions reported from Fort Madison. 
JULY 15, 6.30 a. m.—Only a few mayflies on the dam to-day—comparatively few. 
JuLy 17.—Mr. Howland (assistant general manager, Mississippi River Power Co.) tells me that he 
saw a pile of mayflies in Nauvoo, IIl., this morning that was about 6 feet in diameter and 18 to 20 inches 
deep. When I crossed the dam to-night at about 6.45 p. m. they were quite thick and were coupling 
and mating while flying. Above the chutes of the lock there is an enormous floating mass consisting 
mainly of mixed ephemerid adults, cast skins, and duckweed. 
JULY 18, 5.30 a. m.—As abundant as ever on the dam to-day. A little later —They are more 
abundant than ever this morning. 
JuLy 22.—Still a scattering of these on the dam this morning. 
JuLy 26.—Still a couple of thousand on the dam. Many on train arriving from the north; so it 
is evident they are still coming out on the lake. 
JuLyY 28.—Crossed the dam early this morning and was surprised to find thousands, perhaps 
millions, of the mayflies in the air. I believe that these are nearly ascommonasever. The north end 
of the power house (see Bureau of Fisheries Doc. No. 805, Pl. III) is blackened with them. Workman 
tells me this lot has been here about two days. Night Lock Master Raber tells me the present lot started 
last night. Collected some in process of transformation and some apparently just ready to transform. 
JuLY 30.—Large mass of dead adults above the locks; smell offensive on the lee side. Very few 
on dam this evening (6.15 p. m.), less than a hundred, I think. 
AUGUST I AND 2.—A few, scattering, on the dam. 
AucusT 5.—None on the dam to-day. 
Aucust 8, rr a. m.—A scattering of large, brown ones on the dam this moming—quite a number, 
in fact, for the late forenoon. The shady side of the poles had a dozen or two each; some posts had 
more. 
AuGusT 10.—A good many, but no great masses like those of last month. Collected a few at Fort 
Madison to-day. 
AucusT 12.—Collected some in Burlington, Iowa. 
AucusT 14.—As many on the dam as on the roth; possibly more. 
AUGUST 15 AND 16.—Mayflies still on the dam. 
Aucust 18.—Only a few dozen about the dam this morning. 
Aucust 19.—A hundred or more mayflies on the dam. 
AucGusT 21.—Noticed only one live mayfly. 
AucusT 23.—Again abundant on dam. Many on the gauge house; some on power-house walls; 
the horizontal portions of the dam thick with them, so that at each step one or more are crushed. Here- 
tofore they have been mostly confined to upright surfaces. Not very active; few on the wing, doubt- 
less because of cold. 
Aucust 27.—Did not see any mayflies when crossing the dam yesterday or early this morning. 
AuGUST 29.—Have not seen any more living ones. 
SEPTEMBER 2.—Some of the trolley poles on the dam, of which there are about 40, had 200 or 
300 of large, brown mayflies; nearly all of them had some; few compared with earlier flights. 
SEPTEMBER 15, 8 a. m.—Noticed about two dozen clinging to floor of dam. 
[Observations discontinued.] 
Thus Mr. Stringham’s records show that during the summer of 1916, at least, July 
was the month of the principal flights of this species; that emergence was in waves; 
that successive waves reached their height at about the 13th, 18th, and 23d of the 
month, with falling away in numbers on intervening dates; that subsequent smaller 
waves culminated on the roth and the 23d of August, separated by intervals of entire 
