Pale Swallowtails are the only swallowtails in BC that are white (males) or very pale yellow (females) with black stripes, rather than yellow and black. Pale Swallowtails have a small orange crescent, sometimes missing, at the base of the dorsal hindwing tail. All other tiger swallowtails have a large yellow crescent instead.
The report of Papilio ajax var. marcellus (= Eurytides marcellus) from the Cowichan Valley on Vancouver Island (Fletcher 1899), based on a painting sent to Fletcher by C. de Blois Green, may have been either an accidental introduction or a misidentification based on an aberration of P.eurymedon.
Eggs are yellow green, smooth, and hemispherical in shape. A pink tinge develops around the side of the egg within 1-2 days after oviposition. The day before hatching, the egg turns green brown, with the black head capsule showing through the top. Mature larvae are cylindrical, tapering towards the back. They are apple green, except for the whitish underside. They have eyespots similar to those of the Western Tiger Swallowtail, but the blue central spot is smaller. The blue centre of the Western Tiger Swallowtail eyespot is about 1 mm, that of the Pale Swallowtail is 0.5 mm. Behind the eyespots, the two segments are separated by a broad yellow band followed by a black band. Osmeteria are bright orange. Prepupal larvae turn brown, with bright orange eyes pots with black centres. The pupae are cylindrical, with their greatest diameter near the middle, tapering slightly towards the head and rapidly backwards. The pupae are usually brown, streaked with black and brown, with a dark brown band along each side. Some pupae are green (Edwards 1874-84; Sugden and Ross 1963; CSG).
None. The type locality has been restricted to near Belden, Plumas Co., CA (Emmel et al. 1998b).
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.
Pale Swallowtails are univoltine in BC but multivoltine further south. They are in flight in June and July in southern BC. Eggs are laid singly on the upper surface of the leaves of larval foodplants. Eggs hatch 9-10 days after oviposition, and the larvae eat the egg chorion. The first instar lasts about 5 days, and larvae mature in 5-6 weeks. Pupae diapause over winter. Males patrol along forest edges and openings and stream banks looking for females, and are frequently seen mud-puddling. They hilltop on Vancouver Island (Guppy 1970), but this may be because the tops of the hills are the best forest openings available for patrolling. Larvae from the eggs of an interior population using Ceanothus grew abnormally slowly when fed red alder (R. Ashton, pers. comm.). In captivity, females from the Pendd'Oreille River in the West Kootenay refused to lay eggs on Ceanothus, and then laid eggs only on red alder when a mixture of the two plants was offered the next day (CSG).
The known larval foodplants in BC are cultivated apple,Alnus rubra, Amelanchier alnifolia, Betula, Ceanothus sanguineus, Holodiscus discolor, and Prunus emarginata (Harvey 1908; Dyar 1904b; McDunnough 1927; Jones 1936, 1939, 1942; Sugden and Ross 1963; ACJ; FIS). Red alder is the primary larval foodplant on the coast and Ceanothus the primary larval foodplant in the dry interior (CSG). Outside BC additional foodplants include garden crab apple, Ceanothus fendleri, Crataegus rivularis, Frangula californica, Prunus emarginata, P. ilicifolia, and Rhamnus crocea (Edwards 1874-84; Remington 1952; Emmel 1975; Bird et al. 1995; Scott 1992; ACJ).
Pale Swallowtails occur throughout southern BC, in low- to mid-elevation forest openings and riparian habitats as well as on dry Ceanothus slopes in the interior.
Pale Swallowtails occur from southern BC and AB east to the central Great Plains and south to Baja California and NM.
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:
2021-02-26 10:40:20 PM]
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