Initially we weren’t sure if this was a Two-tailed Swallowtail or a Western Tiger Swallowtail, but received some help from fellow butterfly enthusiasts. According to David J. Ferguson, Contributing Editor for BugGuide, “The best clue [for the Two-tailed] is the black edge of the pupil of the large eye spot, which is a thin line. In Western it should be a thick border.” A member of the Butterflies and Moths of the Pacific Northwest Facebook group adds, “Two tailed for sure. They turn orange when pre-pupae, where Westerns turn black/brown/purplish. The false eyespots are also different between species.”
Like many other swallowtails, the younger larvae resemble bird droppings and the older ones have a bright orange, odorous organ (osmetriums) that can be everted from behind the head when under threat.
These caterpillars commonly feed on chokecherry and ornamental green ash in our area. After achieving maximum chunkiness, they overwinter (diapause) as pupae on the base of trunks or on stems. The large and spectacular butterflies will take flight in late spring/early summer. This species ranges across western North America down into Mexico.
Size: Around 3 inches
Photo by: Carolyn Taber on 8/5/22 in Missoula, MT