44 
2 Percentage, by weight, of average total hauls 
contributed by Chironomidae 
1-3-ft. zone 
Channel 47-ft.zone | 
1915 1920 | 1915 1920 | 1915 1920 
Upper lake 0.08 44.2 2.2 EE 2.6 0 
Middle lake 2.0 20.8 Beil 96.2 3.4 87.5 
Lower lake 0 41.9] 0 84.7 | 0 82.7 
Much as have the sludge-worms, the larvae of the midges have in- 
creased in the past five years in Peoria Lake from an average of half a 
pound per acre and a maximum of one pound—representing at the most 
less than 2 per cent. of the average total haul—to as much as 173 pounds 
per acre and 42 per cent. of the average haul in the river channel between 
Chillicothe and Spring Bay, and to a general average of 26.3 pounds per 
acre for all subdivisions and all zones collected from in the three lakes. 
The largest numbers reached—in the channel of the upper lake—amount- 
ed to 4960 per square yard, 4800 of these belonging apparently to a 
single species of Tubifex, and 160 to a species of an undetermined genus 
of Tubificidae. Both in the channel and in the shallower zones, sludge- 
worms became less abundant southward of the upper lake, though it is 
noted that in the channel of the lower lake the average number per square 
yard in 1920 (183) was more than sixteen times the average figure for 
the upper lake channel (11) in 1915 (table). 
SLUDGE-WORMS (PRINCIPALLY TUBIFICIDAE), 
CHILLICOTHE TO Foor or PrortA LAKE, 1915 ann 1920 
1. Number and weight per unit of bottom area 
Channel 4—7-ft. zone 1-3-ft. zone 
1915 1920 | 1915 1920 | 1915 1920 
Upper lake 11 4960 26 1146 | 37 240 
Average No. | | 
per sq. Middle lake | 0 540 0 36 0 12 
yard 
Lower lake 17 183 0 0 0 144 
Upper lake 0.3 173 1 40 1 8 
Average : 
pounds Middle lake 0 19 0 1 0 0.4 
per acre 
Lower lake 0.6 6 0 0 0 5 
Average weight per acre, all channel collections, 1920, 44.5 lbs. 
es « e “all 4—7-ft.-zone collections, 1920, 14.0 lbs. 
os ‘ 3 “all 1—3-ft.-zone collections, 1920, 4.7 lbs. 
all collections, 1920, all zones, 26.3 lbs. 
ms ss Qe Sines 0.5 Ibs. 
