Western Tiger Swallowtail
Diagnosis: The Western Tiger Swallowtail is very similar to the other tiger swallowtails with its distinctive black stripes on a yellow background. The lunulate submarginal markings on the underside of the hindwing are all yellow, while the submarginal spots on the forewing underside form a band. The uppermost spot on the border of the hindwing above is yellow. Wingspan: 65 to 90 mm.
Subspecies: Only the nominate subspecies rutulus has been found in Canada. A form of the Canadian Tiger Swallowtail, called "arcticus," found in Alaska and Yukon, falls well within the accepted parameters of canadensis and is not rutulus as some authors had speculated (Hagen et al., 1991).
Range: This swallowtail is found throughout the U.S. west of the Rocky Mountains. In Canada, it has been recorded only in southern British Columbia from Vancouver Island east through the lower Fraser River Valley and then north into the Okanagan and Kootenay Valleys. See also Remarks.
Similar Species: West of the Rocky Mountains, where it occurs, it can be confused with the Two-tailed Swallowtail (P. multicaudatus) - rutulus has only one tail - and the Pale Swallowtail (P.eurymedon), which has a creamy-white base colouring to the wings. It is best distinguished from the Canadian Tiger Swallowtail (P. canadensis) by the entirely yellow lunular submarginal spots on the underside of the hindwing. In canadensis at least some, if not all, of these spots have orange colouring. The uppermost spot on the border of the hindwing is orange in canadensis but yellow in rutulus. [compare images]
Early Stages: The larva is similar to that of glaucus but feeds on a slightly less varied diet of trees and shrubs than its eastern counterpart, mainly willow, poplar, and birch.
Abundance: It is generally common in its Canadian range.
Flight Season: This depends on altitude; adults appear in May in lower areas and in June and July at higher altitudes.
Habits: This butterfly tends to stay close to water, along canyons, creeks, and into urban parks. It is an avid mud-puddler, usually outnumbering other swallowtails at wet spots where they occur together.
Remarks: In the Okanagan and Kootenay Valleys, the only places in North America where four tiger swallowtail species occur together, hybrids between rutulus and canadensis occur (Brower, 1959). Hybrid specimens, some of which are similar to rutulus in most characters, have been the source of reports of this species beyond its range (e.g., in southwestern Alberta).
© 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.
- Date modified: