EMERGENCE PATTERNS OF THE SUBALPINE 
DRAGONFLY SOMATOCHLORA SEMICIRCULARIS 
(ODONATA: CORDULIIDAE) 
By Ruth L. Willey* 
University of Illinois at Chicago Circle 
Introduction 
The genus Somatochlora is circumpolar and many of its species 
reach high into the subarctic and subalpine regions. S. semicircularis 
occurs in the Canadian and Hudsonian zones of the North American 
Western Cordillera from Alaska to Colorado. Towards the southern 
part of its range, this species is found at high altitudes in Colorado 
where adults have been recorded at 3000 to 3700 m (Gloyd, 1939; 
Walker, 1925; Carpenter, 1873). Larval habitats range from 2700 
to 3600 m in shallow ponds and water meadows. These may well be 
the highest breeding localities for any odonate known. 
The alpine and subalpine habitats offer extremes in temperature 
and insolation during the short growing season which follows the late 
snow melt (Mani, 1968). The subalpine regions, particularly, pre- 
sent relatively the highest day and lowest night temperatures (Bill- 
ings and Mooney, 1968). Coupled with these factors, the frequent 
periods of drought and general unpredictability of climate contribute 
to the rigor of the high altitude habitat. Studies of life history strat- 
egies of insects which have adapted to high altitudes have revealed 
cold resistance and lowered temperature thresholds, a predominance 
of diurnal activity, a seasonal delay and shortening of the flight 
period, and a general increase in the length of the life cycle coupled 
with overwinter hibernation or diapause (Mani, 1968). In the 
dragonflies, the increased life cycle is accomplished by elongating the 
larval period to as much as three or four years (Paulson and Jenner, 
1971; Robert, 1958). Somatochlora semicircularis larvae are also 
resistant to dessication when their ponds and water meadows dry up 
annually (Willey and Eiler, 1972). An ecologically sensitive part 
of the life history for a dragonfly is the emergence period during 
which the “aquatic” larva leaves the water, transforms into the 
^Department of Biological Sciences, University of Illinois at Chicago 
Circle, Chicago, Illinois 60680; and The Rocky Mountain Biological Labora- 
tory, Crested Butte, Colorado 81224. 
Manuscript received by the editor February 7 , 1974. 
2 
