The final instar larva of S. sahlbergi is redescribed using material collected in the Yukon Territory, Canada. Differences between this larva and those of its closest Nearctic relatives, S. albicincta and S. hudsonica, are outlined and a key to the larvae of the alpestris group of Somatochlora is provided. S. sahlbergi is an amphi-Beringian species, distributed across northern Asia in a band near the northern limit of trees, but in North America is found only in the extreme northwest. It is usually found in deep, cold, mossy ponds. Examination of larval morphometries indicates a four to five year maturation period. In the northern Yukon and adjacent Northwest Territories, 5. sahlbergi hybridizes with 5. albicincla and S. hudsonica.