Its appearance is similar to the western, and eastern tiger swallowtails, but has narrower black stripes and usually two tails on each hindwing (rather than only one).

Most two-tails have a black "slit pupil" in the orange eyespot on each hindwing, never present in western tiger.

The wingspan ranges from 3 to 6.5 inches (7.6 to 16.5 cm), making it the largest swallowtail in western North America.

[5] Males may engage in mud-puddling, and have claspers that can be seen as a yellow segment at the end of the abdomen, beyond the black abdominal stripes.

[2] It does not tend to hybridize with related species as do the western, eastern, and Canadian tiger swallowtails.