Large Marble (Euchloe ausonides) (Lucas, 1852)
Diagnosis: This is the largest (wingspan: 30 to 48 mm) of the five marbles found in Canada. The underside of the hindwing usually has more white shading than green, with the white shading forming large irregular spots that partially fuse together through the reticulate green pattern; the veins are usually lined with yellow, and this extends through the green pattern. On the upper surface of the forewing the dark discal spot in the middle of the leading edge of the wing is black, with an extensive dusting of white scales (best seen with a microscope or a 15x hand lens). The discal spot is narrow in males, with the apex (projecting towards the middle of the wing) pointed or rounded; in females it tends to be broader, with the apex squared off, but the upper surface of the hindwing often has a slightly yellow cast in females, unlike the other marbles.
Subspecies: Four subspecies are currently recognized, but none of these is very distinctive. The holotype of subspecies mayi in the Canadian National Collection, from Riding Mountain, Manitoba, is barely distinguishable from Californian specimens (nominate ausonides), and we treat all Canadian populations, except as discussed below, as subspecies ausonides. Two populations in Canada not currently treated as subspecies are more distinctive. Specimens from southern Vancouver Island are large (41 to 48 mm) and have more extensive green on the underside of the hindwing and very dusky females. This unnamed population apparently is extinct. Specimens from northern Yukon and Alaska were recently described as a new species (Euchloe ogilvia Back, 1990). This species, described from the Ogilvie Mountains, Yukon, was based on slight differences in pupal shape and egg microsculpture as compared with material from San Francisco. It is also diagnosed as having more extensive green shading on the underside of the hindwing with little yellow scaling on the veins. A complete range of intergradation between these extremes occurs in the southern half of Yukon, so we treat ogilvia as a northern subspecies of ausonides.
Range: The Large Marble is found throughout most of western Canada as far north as treeline. It is absent from the west coast (extinct on southern Vancouver Island) and from the open prairie regions of southern Saskatchewan and Manitoba. Its range extends eastward into Ontario as far as Manitoulin Island.
Similar Species: The Desert Marble (E. lotta)has the discal spot solid black (the margin of the spot may be fuzzy, but there is no white speckling on the spot); the spot is broad, with the apex abruptly squared off where it ends at a wing vein in both sexes. The underside is similar to that of the Large Marble, but in Canada the green reticulate pattern is broader so that the green shading covers more of the wing than the white shading. The Green Marble (E. naina) is similar to E. ausonides ogilvia, but the green shading is even more extensive, so that the hindwing underside is almost entirely green with white shading limited to a few white patches on the leading edge of the wing and along the outer margin. The Northern Marble (E. creusa) tends to be smaller than ausonides (24 to 36 mm versus 30 to 48 mm) and the white shading on the hindwing is in long, narrow streaks that run parallel to the outer margin of the wing; the effect is a streaked or banded pattern rather than a blotchy pattern. The Northern Marble, like the Desert Marble, has few if any white specks in the black discal spot on the upperside of the forewing and the spot is frequently truncate, although it is usually narrower than that of lotta. The Olympia Marble (E. olympia) is readily identified by the reduced green shading on the underside of the hindwing. The Large Marble is the only marble that frequently has a pale yellow hind wing in the female; this is rare in creusa and apparently absent in the other three species. [compare images]
Early Stages: The larva is dark bluish grey with many black dots and length wise bands of yellow and white. It feeds on a wide variety of members of the mustard family, including Tower Mustard (Arabis glabra) and Tumble Mustard (Sisymbrium altissimum).
Abundance: Although widespread, this butterfly is localized to generally open forested areas, particularly around pines. Populations often fluctuate in numbers from year to year.
Flight Season: In southern British Columbia, the Large Marble flies in April and May, while in Manitoba it has been recorded from early May to late July. It tends to fly later in mountainous areas.
Habits: Perhaps this butterfly is best looked for in sandy areas in open pine forests, where it flies with a relatively slow zigzagging pattern.
Remarks: A specimen of the Large Marble in the CNC was collected in 1887 near Dease Lake along the Cassiar Trail in northern British Columbia by G.M. Dawson, for whom Dawson, Yukon, is named.
© 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.
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