Canadian Tiger Swallowtails are yellow with black bands running from front to back across the wings. The spots in the black margins on the dorsal hindwings are mostly yellow, but the first spot is always orange (in contrast to the Western Tiger Swallowtail), except that sometimes it is missing entirely. These marginal spots are all partly or entirely orange on the underside of the hindwing. The blue markings on the underside of the hindwings are much more developed in the Canadian Tiger Swallowtail than in the Western Tiger Swallowtail. There is a zone of hybridization with the Western Tiger Swallowtail where their ranges overlap.
For many years the Canadian Tiger Swallowtail was considered to be a subspecies of the Eastern Tiger Swallowtail. Recently Hagen and Scriber (1991) and Hagen et al. (1992) demonstrated that they are separate species that fly together in southern Ontario. Eastern Tiger Swallowtails are bivoltine and can mature more successfully on different larval foodplants than Canadian Tiger Swallowtails (with some overlap). Many pupae of hybrids die rather than produce adults.
The eggs are green, approximately hemispherical, and smooth. Mature larvae are velvet green with eyespots on their middle thoracic segment and a yellow and black stripe between that segment and the next. The eyespot on each side of the thorax of a mature larva is yellow, outlined in black and bisected by a black line. A black line encloses a blue centre spot, and the black transverse band is narrower than the anterior yellow band and does not extend to the spiracular line (Sugden and Ross 1963). The osmeteria are orange (CSG) and the prepupal larvae turn dark reddish brown (Saunders 1869c). Pupae are light brown with a darker brown lateral stripe, two short horns on the head, and a peak at the top of the thorax.
Canadian Tiger Swallowtails were originally described from Newfoundland. There are no recognized subspecies. Papilio rutulus arcticus Skinner was published in December 1906 and is a synonym of P. canadensis, which was published in August 1906 (Martin Honey, pers. comm.).
Linnaeus divided butterflies into several groups. The first group was the swallowtails, which were called equites or knights. Those with red on the thorax were Greek heroes, those with no red on the thorax were Roman heroes (Emmet 1991). Papilio, which is Latin for butterfly, was the original generic name that Linnaeus used for all butterflies. The common name was first used in Britain in 1766 for "The Swallowtail," P. machaon (Bretherton 1990b), in reference to the resemblance of the tails on the hindwings to the tails of swallows. The name was later extended to include the entire genus. Gosse (1840) was the first to use the common name "swallowtails" in North America.
Swallowtails found in North America are large, brightly coloured butterflies with tails on their hindwings. Six of the eight species in BC are yellow with black stripes. In addition, Pale Swallowtails are white to very pale yellow with black stripes, and Indra Swallowtails are mostly black. Swallowtails also have an orange eyespot at the base of each hindwing tail, and orange and blue spots on the ventral hindwings.
Eggs are smooth and hemispherical, and are cream, yellow, yellow green, or green when laid. The egg colour darkens, and a red ring develops around the top before hatching. Young larvae are black with a white saddle, and resemble bird droppings. Larvae of all ages have well-developed osmeteria, extrusible Y-shaped glands on the top of the thorax that produce defensive chemicals in response to attack. Pupae have two small horns on the head and a point at the top of the thorax. A silk girdle holds them head up against a stem.
The eggs are laid on the leaves of the larval foodplants. On plants with large flat leaves, the eggs are laid on the top or occasionally just under the leaf edge. Both the top and bottom of small leaves are used. The pupae overwinter. In BC two species have more than one generation each year in some populations; the other six are univoltine.
Hancock (1983) split the genus Papilio into six genera, two of which (Papilio and Pterourus) are in BC. We treat Hancock's genera as subgenera of a single large genus, Papilio, as do most recent authors.
Higgins (1975) suggested that the North American populations of Old World Swallowtails may not be the same species as Papilio machaon. Eitschberger (1993) found that the rings of plates surrounding the egg micropyle are significantly different between one European machaon subspecies and subspecies aliaska, the North American subspecies closest to European machaon. European P. machaon has 3 rings with about 112 plates around the micropyle, while aliaska has 5 rings with about 142 plates. A second character used by Eitschberger to separate P. machaon from aliaska, the number of teeth on the harpe of the male genitalia, is not useful in separating species in North America. The difference in egg structure is insufficient to split the species without additional data, hence we continue to treat the North American populations as subspecies of Papilio machaon.
All the tiger swallowtails (subgenus Pterourus) hybridize in the wild to some extent. In southern BC there is a broad zone of hybridization between Canadian Tiger Swallowtails and Western Tiger Swallowtails from Manning Provincial Park east to Creston. In the areas where their ranges overlap, Western Tiger Swallowtails prefer low-elevation deciduous forest habitats whereas
Canadian Tiger Swallowtails prefer higher-elevation boreal forest habitats. Hybridization between Pale Swallowtails and Western Tiger Swallowtails is rare, but Wagner (1978) collected a perfectly intermediate male hybrid in the wild in Idaho. Jon and Sigrid Shepard found a male hybrid of the Pale Swallowtail and the Canadian Swallowtail 10 km south of Galloway, BC. lt is intermediate in appearance between the two species.
Similarly all the Old World swallowtails (subgenus Papilio) occasionally hybridize in the wild. The Old World swallowtail species are most easily distinguished by the overall coloration of the hindwing and by the colour of the eyespot at the base of the tail on the hindwing.
Canadian Tiger Swallowtails are univoltine. They are in flight from May to July at low elevations, and until August at higher elevations. Eggs are laid singly on the upperside of the leaves of larval foodplants, and hatch in 7-10 days. Pupation occurs in another 6-8 weeks, and pupae diapause over the fall and winter. The males patrol forest openings and stream banks looking for females, and are frequently seen mud-puddling.
In BC larval foodplants include alder, birch, black cottonwood, trembling aspen, and willow (Sugden and Ross 1963; CSG; FIS). Outside BC other larval foodplants include ash, cherry, cultivated apple, and cultivated crab apple (Fletcher 1889c; Ferguson 1954; Brower 1959; Bird et al. 1995).
Canadian Tiger Swallowtails are found throughout southeastern, central, and northern BC in predominantly boreal forest habitats. They occur in coniferous forest and aspen grove habitats.
Canadian Tiger Swallowtails are found from AK south to southeastern BC, and east across to NF. East of the Rocky Mountains, the species extends south into the northern USA.
Recommended citation: Author, Date. Page title. In Klinkenberg, Brian. (Editor) 2019. E-Fauna BC:
Electronic Atlas of the Fauna of British Columbia [efauna.bc.ca]. Lab
for Advanced Spatial Analysis, Department of Geography, University of British
Columbia, Vancouver. [Accessed:
22/11/2019 11:56:31 AM]
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