Labrador Sulphur (Colias nastes) (Boisduval, 1834)

Diagnosis: Slightly smaller (wingspan: 28 to 42 mm) than most other sulphurs, this species is also more greenish than yellow on the upper surface, with a heavy dusting of dark scales. The male is unique in having light markings in the dark margin similar to the female. Below, the silvery cell spot has a smeared red margin.

Subspecies: Four subspecies are recognized in North America: the nominate subspecies nastes occurs in northeastern Canada and the high Arctic; subspecies moina occurs on the west coast of Hudson Bay; subspecies aliaska occurs in the western Arctic, Yukon, and Alaska; and subspecies streckeri occurs in the Rocky Mountains of Alberta and British Columbia.

Range: This is an arctic species of northern Eurasia and North America. In Canada, it occurs southwards in alpine areas to the U.S. border in British Columbia and Alberta. It is found across Yukon, Nunavut and the Northwest Territories into the Arctic Islands as far as Ellesmere Island. It has been recorded on both the east and west coasts of Hudson Bay and in Labrador.

Similar Species: The green form of Booth's Sulphur (C. tyche) is similar, but is larger and lighter in colour. [compare images]

Early Stages: The green larva has lighter side stripes with a red edge. It feeds on arctic legumes, including Alpine Milk-vetch (Astragalus alpinus) (Pyle, 1981).

Abundance: The Labrador Sulphur can be fairly common, but is frequently overlooked because of its green colour and low, rapid, moth-like flight.

Flight Season: Adults fly from June to mid-September depending on location. In Labrador and Alberta it is most often found in July and August.

Habits: The Labrador Sulphur is generally found at higher altitudes than most other sulphurs. They favour windswept, rocky ridges and dry gravelly hilltops, and occasionally land on the ground with their closed wings at right angles to the sun to absorb the warmth before flying again. The combination of dark-green colour, rapid low flight, and the windy conditions where they occur can make them difficult to spot and follow.

© 2002. This material is reproduced with permission from The Butterflies of Canada by Ross A. Layberry, Peter W. Hall, and J. Donald Lafontaine. University of Toronto Press; 1998. Specimen photos courtesy of John T. Fowler.