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Adults are very large (90-127 mm wingspan). They are easy to distinguish from other swallowtails in Alberta by their size and because each hindwing has two tails, one twice as long as the other. The most similar species in Alberta is the Canadian Tiger Swallowtail (P. canadensis), which is smaller, has wider black bands and lacks the additional tail. Larvae are apple green and have two eye-spots near their head. They have a yellow green to yellow main eyespot with a pale blue centre, it is surrounded by a black line. The adjacent satellite spot is also yellow green to yellow and is enclosed by a black line. There is a yellow anterior band that is narrower than the black transverse band (Guppy & Shepard, 2001). A few days before pupating, the larvae turn red-brown. Pupae are mottled green brown to yellow brown, with a brown lateral stripe (Guppy & Shepard, 2001).

Adults are known to mud-puddle. Males patrol stream courses, lake margins, forest edges and openings, and city streets looking for receptive females [Opler et al., 1995]). Females lay eggs singly on leaves of host plant (Guppy & Shepard, 2001). Larvae hatch, consume the egg chorion, eat leaves and rest on silken mats in shelters of curled leaves (Opler et al., 1995; Guppy & Shepard, 2001). Eggs are pale green yellow (Guppy & Shepard, 2001). They are univoltine and the pupae overwinter (Opler et al., 1995; Guppy & Shepard, 2001; Anweiler, pers. obs.).

Unknown for Alberta. Elsewhere, cherries (Prunus spp.), ashes (Fraxinus spp.), hop tree (Ptelea trifoliata), chokecherry (Prunus virginiana) and Saskatoon (Amelanchier alnifolia). Adults feed on flower nectar and in Alberta they have been observed feeding on thistles (Carduus spp. and Cirsium spp.) and Wild Bergamot (Monarda fistulosa) (Lancaster, 1988; Sperling & Kondla, 1991; Bird et al., 1995).

Other Canadian records are from southern British Columbia and southwestern Saskatchewan (Layberry et al., 1998). It has a wide range in the western United States, south through Mexico and Central America to Ecuador, South America (Opler et al., 1995).