Caddisfly Life History 
111 
2 . 8 - 
2 . 6 - 
2 . 4 - 
2 . 2 - 
E 
E 
1 . 8 - 
1 . 6 - 
1 . 4 - 
1 . 2 - 
1 . 0 - 
75 % 
rh 
IV.-V* 
14 % 
FALL WINTER SPRING 
N D M 
20 11 43 
Fig. 2. Seasonal variation of head width in P. postica larvae. Horizontal lines = 
means; vertical lines = ranges; open rectangles = one standard deviation; shaded 
rectangles = standard error of the mean; letter = month; number = sample size; 
and % = growth rate. 
weeks, however, before adding another anterior ring (Fankhauser and 
Reik 1935). 
The larvae in our study were largely carnivorous early in their life 
cycle, shifting to a more omnivorous diet in later stages (Table 1). The 
diet of larvae collected in the fall consisted primarily of the copepod, 
Cyclops sp. (x= 4.82 per foregut, 85 percent frequency of occurrence (% 
FO) ). Ostracods (x = 2.1 per foregut, 50% FO), diatoms (x = 0.42 per 
foregut, 20% FO), and detritus (x = 11.55 per foregut, 100% FO) were 
also found. In winter, the larval diet consisted primarily of Cyclops sp. 
and ostracods (x = 4.33 and 2.33 per foregut, respectively, 55% FO for 
each). Diatoms (x = 1.19 per foregut, 73% FO) and detritus (x = 18.39 per 
foregut, 100% FO) were also found in winter. The larval diet shifted 
in spring and consisted primarily of ostracods and midge larvae (x = 
4.5 and 2.0 per foregut, respectively, 20% FO for each). Detritus (x = 
27. 12 per foregut, 100% FO) and diatoms (x = 0.90 per foregut, 62% FO) 
were also found during this season. 
