28 
Psyche 
[March 
dragonflies until the second week of emergence. On cold and stormy 
days, loss may approach 100% at any time during emergence. 
Adults which have transformed but have been prevented from flying 
by low temperatures or rainy weather may remain clinging to the 
sedges for a day or more. Most of these adults fall prey to birds. 
Once the tenerals fly, they are reasonably free from bird predation. 
Only one teneral has been observed to be caught by a bird (Western 
flycatcher) during its maiden flight. 
Discussion 
Somatochlora semicircular is is a western cordilleran dragonfly 
whose adults normally appear between the middle of June and the 
middle of July (Walker, 1925). The Colorado ponds under in- 
vestigation occur at the southern limit of the species and yet the 
adults emerge in early July and appear as reproductives in mid-July 
near the end of the general emergence season. Such a relatively late 
season is probably correlated with the late snow melt and low tem- 
peratures of its high altitude habitat. Schiemenz (1952) has reported 
a similar delay of season correlated with altitude for Libellula quad- 
rimaculata. 
Dragonfly emergence has been shown to be temperature-dependent 
with the initiation of emergence primarily dependent on water 
temperature (Trottier, 1973; Corbet, 1963). The larvae of S. 
semicircularis in Colorado first leave the water when the water 
temperatures average I2°C. and the air temperatures average 9°C. 
Comparative data for other corduliid dragonflies are not available. 
The only data available come from the studies of the aeschnid dragon- 
fly Anax. Corbet (1957) found that A. imperator in England nor- 
mally left the water when the temperature reached 19 0 to 22°C. 
(air temperature, 12° to I5°C.). Trottier (1973) found that A. 
junius in Ontario, Canada, normally initiated emergence when the 
water temperature reached 24°C. (air temperature, 15 0 to 20°C.). 
At water temperatures below I7°C., the Anax larvae which had left 
the water would return to the water and delay emergence until the 
following day. The Somatochlora larvae were able to leave the water 
and undergo transformation at average temperatures 5°C. below the 
minimum for A nax larvae. Whether this difference is a specialization 
to high altitudes or is only a general family difference must be further 
investigated. 
In general, teneral corduliid dragonflies at lower altitudes and/or 
latitudes are ready to fly early in the morning. However, the emer- 
