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Somatochlora sahlbergi
Treeline Emerald
Family: Corduliidae
Species account author: Robert Cannings.
Extracted from Introducing the Dragonflies of British Columbia and the Yukon (2002)
Introduction to the Odonata of BC
The Families of Odonata of BC

Photograph

© Robert A. Cannings     (Photo ID #1058)

Species Information


Description

Closely related to the Hudsonian and Ringed emeralds, but lacks the abdominal rings. Similar also to the Quebec Emerald, but their ranges do not overlap. The thorax sides are coppery-green, usually without obvious marks. Male’s appendages, shown in figure. Female’s vulvar lamina shown in figure. (Hybrids with Ringed and Hudsonian emeralds can confuse identification; their sizes, abdominal rings and appendage shapes are intermediate between those of the parent species.) Length: ♂ 50 mm, ♀ 48 mm.


Flight Period

Yukon, late June to late August.

Genus Description


The scientific name comes from two Greek words: soma, meaning “body”, and khloros, meaning “green”. The English name refers to the yellow or white markings on the sides of the metallic green or bronzy thorax, but most of the distinctly striped species live in eastern North America; western species have spots, short bars or no marks at all. They all have brilliant green eyes. Most North American species are boreal and Appalachian; 13 of 26 occur in our region. Most live around northern or mountain lakes and peatlands.

Species can be hard to identify, especially the females. Look for pale marks on the side of the thorax and white rings between the segments of the abdomen. Hudsonian, Ringed and Lake emeralds have narrow, white abdominal rings. Examine the shapes of the male’s upper appendages and the female’s vulvar lamina. And look for a brown spot at the base of the hindwings – not the membranule, which can also be dark, but an additional spot (Delicate, Muskeg and Whitehouse’s emeralds have it).

Biology

Family Description

Medium-sized dragonflies most often seen around lakes, boggy streams and peatlands in the mountains or in the north. Of 16 species in our region, 13 have Northern or Beringian ranges. The eyes, often brilliant green, meet broadly on top of the head. The shape of the anal loop in the hindwing is distinctive. Adults seldom perch during feeding and males frequently hover when patrolling for mates; when resting, they normally hang vertically or obliquely from vegetation. In flight, a male frequently arches its abdomen, which is often narrower at the base and tip. Larvae are usually squat and rather hairy; they sprawl in the mud and detritus in the bottom of the waters where they live.
Field Notes

Has the most northerly breeding range of any dragonfly: as its name suggests, the Treeline Emerald lives within 100 km of the Arctic treeline and within 300 metres of the altitudinal treeline. It inhabits a range of ponds and pools, from roadside ditches to moss-margined lakes. All habitats have two main characteristics: aquatic mosses as the dominant vegetation, and deep, cold water. Males and females tend to fly out over the water rather than circle the pond margins as Hudsonian and Ringed Emeralds do. The Treeline Emerald interbreeds with both these relatives where they occur together.

Distribution


East Beringian, and across northern Eurasia. Northern Yukon from the Blackstone River to the Porcupine River drainage.

Status Information

Origin StatusProvincial StatusBC List
(Red Blue List)		COSEWIC
UnlistedUnlistedUnlistedUnlisted



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