1974 ] 
Willey — Subalpine Dragonfly 
123 
lined with Isoetes bolanderi on the bottom. The pond is surrounded 
by a belt of forb-sedge meadow which is surrounded by an open 
association of spruce-fir ( Picea engelmanni and Abies lasiocarpa ) 
(Fig. 1). In the past eleven years of observation, Pond Nine has 
never totally dried up. 
Irwin Pond South (3141 m) lies near the edge of Lake Irwin 
(Lake Brennan) near Kebler Pass in Gunnison Co., Colorado. Its 
basin is 45 m in diameter, 1.2 m deep in June and dries up in late 
August and early September (observed 1968-1973). The shoreline 
and shallow areas where emergence takes place are lined with C. 
rostrata and C. aquatilis. The deeper areas support Potamogehon 
foliosus and P. illinoisensis and thin mats of Drepanocladus uncinatus. 
This pond has been described further by Willey and Eiler (1972). 
Materials and Methods 
The emergence of Somatochlora semicircularis was studied from 
1968 to 1972. At first, the transforming larvae were marked by 
surveyor’s flags so that the transformation of each individual could 
be accurately timed. Considerable trampling of the habitat was un- 
avoidable so that the studies were repeated in 1971 by making daily 
collections of the cast skins left behind by the teneral adults. Fewer 
larvae were damaged during their transformation by this method. 
However, more larvae were lost through bird predation so that their 
cast skins could not be recorded. In order to verify the diurnal 
pattern of the teneral flight in an undisturbed habitat, continual 
observations by binoculars of the ponds were conducted from 100 
feet away from the shoreline in 1972 during the peak of the emer- 
gence period. 
Water temperatures were measured 3 cm below the water surface 
in areas of highest emergence activity. Solar radiation was measured 
by a recording Belfort pyrheliograph with a 12-hour gear. Environ- 
mental air temperatures were measured with a YSI telethermometer 
shielded from radiation by thin, flat, double-layered shields, 46 cm 
square, which were set horizontally 8 cm above and below the tem- 
perature probe. The inner surface of each was painted flat black and 
the outer surface was glossy white (Platt and Griffiths, 1964). 
Observations 
About one month after the ice leaves the ponds, the first larvae of 
S. semicircularis leave the water, undergo transformation, and fly 
