Caddisfly Life History 
109 
case were measured to the nearest 0.05 mm. The mean, range, standard 
deviation, and standard error of the mean were calculated for these 
values. The regression analysis of case length on total length of larvae was 
calculated and a coefficient of correlation determined. 
In order to find the pupal stage, the swamp bottom was scraped for 
mud and debris with a long-handled dredge net of mesh size 60 threads/ 
inch. Submerged logs were examined by pulling away rotting bark and 
loose pieces of vegetation to uncover pupal cases embedded in soft wood. 
Cases were preserved in 70 percent ethanol. Adults were collected with a 
Ward’s ultraviolet light trap (8 watts) and with a fluorescent tube light 
placed on a sheet, then preserved in 70 percent ethanol. 
RESULTS AND DISCUSSION 
Water quality. — The pH ranged from 6.0 in February to 7.7 in March; 
x= 6.7. Dissolved oxygen concentration ranged from 2.0 to 12.0 mg/ 1 in 
July and January, respectively. Carbonate alkalinity values ranged from 
17.1 mg/1 in January and February to 85.5 mg/ 1 in May, June and 
September; x = 57.0 mg/l. Total hardness ranged from 51.3 to 205.2 
mg/ 1 in February and July, respectively; x = 107 mg/l. Mean annual 
temperature for the study period was 9.8° C, with extremes of 0° C from 
December through February and 30° C in September. 
Larval stage. — Length-frequency histograms indicated that this popu- 
lation contained one size class (Fig. 1). The earliest and smallest larvae 
were collected in November 1978 (x length = 13.3 mm, R= 9.0-20.0 mm). 
The last and largest larvae were collected in March 1978 (x length = 30.7 
mm, R= 27.0-34.5 mm). 
Head width was used to show seasonal variation in growth (Fig. 2). 
Larvae grew most rapidly from fall (November) to winter (December) (x 
head width in fall = 1.2 mm, R = 0.96-1.65 mm; x head width in winter = 
2.06 mm, R= 1.39-2.44 mm). They increased their mean head width by 75 
percent over the two-month period. The largest mean head width, 2.38 
mm, was in the spring (R = 2.18-2.57 mm). Larvae increased their mean 
head width by 14 percent from winter to spring. Growth was retarded 
during winter, when water temperatures were at their lowest and the 
swamp was frozen over. 
We tried to determine the number of larval instars by using head width 
measurements (Fig. 3). The graph shows a definite grouping of head 
widths, indicating three different instars. However, no larvae were found 
from July to October. This could eliminate one or two instars from the 
calculations. 
Siltala (1907) and Wesenberg-Lund (1911, 1913) stated that the larvae 
of European phryganeids grow rapidly during summer and early fall, and 
reach the last larval stage in October. In this stage they pass the winter 
