Arrowhead Blue (Glaucopsyche piasus) (Boisduval, 1852)

Diagnosis: The male upperside is bright blue with wide, dark borders diffusing into the blue, and checkered black and white fringes. The female is duller in colour. The underside is pale grey, with a median row of black spots and a row of grey chevrons near the margin on both wings. There is a row of white "arrowheads" pointing inward, between the row of black spots and the row of grey chevrons on the hindwing. Wingspan: 25 to 32 mm.

Subspecies: There are several subspecies described, of which two are found in Canada: subspecies daunia occurs in Alberta and Saskatchewan and is darker blue above than subspecies toxeuma,which is found in southern British Columbia.

Range: Glaucopsyche piasus flies in the western U.S., reaching Canada only in southwestern Saskatchewan, southern Alberta, and the southern interior of British Columbia, as far north as Pavilion Mountain.


Specimen collection data


Similar Species: The Silvery Blue (G. lygdamus) lacks the second row of underside spots; both it and the Greenish Blue (Plebejus saepiolus) lack the white arrowheads. [compare images]

Early Stages: Eggs are laid singly on buds, leaves, and stems of the foodplants, and the larvae eat all parts of the plant. They vary in colour from yellow-brown to various shades of green, with reddish or pale dorsal lines and oblique stripes; they hibernate as pupae. Foodplants are various species of shrubby and herbaceous Fabaceae, especially lupines (Lupinus spp.).

Abundance: The Arrowhead Blue is locally common, although it is often absent from seemingly suitable areas where the foodplant is abundant.

Flight Season: Adults fly from late May to early July; there is one generation per year.

Habits: The preferred habitat of the Arrowhead Blue is prairie, open woodland, and woodland edgesand trails. The only known Saskatchewan colony is on the prairie at the foot of the hillside bordering Belanger Creek on the south side of the Cypress Hills.

© 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.