Silvery Blue
Glaucopsyche lygdamus (Doubleday, 1841)

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Diagnosis: The upperside is a shiny light blue, with a dark grey border around both wings, wider in the female and sometimes suffusing the entire wing surface with grey. The underside is grey, with a single row of round, black, white-rimmed spots on both wings. Wingspan: 18 to 28 mm.

Subspecies: About a dozen subspecies have been named, but we recognize only one as occurring in Canada. Subspecies couperi was named from Anticosti Island, Quebec, and is found throughout the rest of Canada. The nominate subspecies lygdamus is found locally in the eastern U.S., and was once reported from Point Pelee, Ontario, but this specimen has now been reidentified as subspecies couperi (Alan Wormington, pers. comm.).

Range: Glaucopsyche lygdamus is found over much of the U.S., extending farther south in the west. In Canada it occurs in every province and territory, but is absent, except for a few old records, from southwestern Ontario; Ancaster, west of Toronto, appears to be the present southern limit for subspecies couperi. Its range extends north to Kuujjuaq (Fort Chimo), Quebec, Churchill, Manitoba, and Coppermine, Nunavut and Tuktoyuktuk, Northwest Territories.

Similar Species: The Arrowhead Blue (G. piasus). The Greenish Blue (Plebejus saepiolus) and Boisduval's Blue (Icaricia icarioides) have two rows of small black spots on the underside of both wings. [compare images]

Early Stages: The eggs are laid on flower buds of the foodplant, timed so that the newly emerged larvae can feed on newly opening flowers. The larval colour depends on their food, varying from whitish or purple, if feeding on flowers, to green when eating leaves, always with a darker dorsal stripe and pale diagonal stripes on the sides. The larvae are often attended by ants. The foodplants, always Fabaceae, can vary widely; in the east they are usually common non-native plants such as Cow Vetch (Vicia cracca), White Sweet Clover (Melilotus alba), and Alfalfa (Medicago sativa). In Manitoba, wild pea (Lathyrus spp.), milkvetch (Astragalus spp.) and trefoil (Lotus spp.) are used, while on Cape Breton Island, larvae have been found on Beach Pea (Lathyrus japonicus). Hibernation is as a pupa.

Silvery Blue (Glaucopsyche lygdamus couperi) male. Low, Que. P.W. Hall

Abundance: This species is often abundant.

Flight Season: In the south, the single generation flies from early May to early July. In Newfoundland and the north, the emergence period is extended and the season runs from mid-June to at least mid-August.

Habits: The Silvery Blue has quite a strong flight, and is usually seen visiting flowers or on the ground in damp areas. It is most commonly seen in open woodland, flowery meadows, and roadsides, sometimes in small waste areas in cities. In places it seems to be expanding its range along roads following the spread of non-native plants such as Cow Vetch.

© 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.

The Toronto Entomologists' Association thanks Agriculture and Agri-Food Canada for providing the content and computer code for this web page.