Papilio eurymedon

Pale Swallowtail

The pale swallowtail is similar to the western tiger, but usually much closer to white than yellow in ground color, and also less likely to be found in urban or suburban areas. In addition, the pale swallowtail is an avid hilltopper, unlike the western tiger. In some cases, I've found that lighter (or worn) western tigers are easy to confuse with pale swallowtails (especially those that are somewhat yellowish) in places both may fly. If the ground color doesn't help, I've found that the thickness of the black border is a pretty good indicator: it's wider in the pale swallowtail. The tails of eurymedon should be half-turned, though that doesn't always hold up.

Its larval food plants differ very much from P. rutulus, which feeds on various common trees such as sycamores and ash. P. eurymedon uses shrubby members of the Rose and Buckthorn families, such as Prunus ilicifolia, Rhamnus ilicifolia, and some species of ceanothus such as cuneatus. The pale swallowtail is single-brooded, with early larval instars looking like unappetizing bird poop, and the last instars green with false eye-spots. So they are generally similar to the larvae of rutulus, but found on very different host plants.

For the original scientific description, see below and check out the page for rutulus as well for the fuller story. In the 1998 Systematics publication (p.78), Emmel, Emmel, and Mattoon resticted the type locality to the Queen Lily Campground, near Belden in Plumas Co.

Pale Swallowtail - Papilio eurymedon
A pale swallowtail posing streamside on a trail in Big Tujunga Canyon, San Gabriels. May 16, 2006. This is all I ask of our butterflies: be fresh and stay still.
Pale Swallowtail - Papilio eurymedon
This pale swallowtail was also near a stream, but in the Santa Rosas above Palm Desert. May 14, 2006. The left wing was a bit malformed.
Pale Swallowtail - Papilio eurymedon
Close-up of the same pale swallowtail above.
egg of a Pale Swallowtail butterfly - Papilio eurymedon
I found this eurymedon egg on host Prunus ilicifolia on Cactus Spring Trail on June 12, 2020.
third instar caterpillar of a Pale Swallowtail butterfly - Papilio eurymedon
The day after finding the egg above, I found a third instar larva on Prunus ilicifolia off Santa Rosa Truck Trail. June 13, 2020.
fourth instar caterpillar of a Pale Swallowtail butterfly - Papilio eurymedon
Same as above, but looking like it's ready to molt from the fourth to the fifth instar. July 2, 2020.
Chrysalis of a Pale Swallowtail butterfly - Papilio eurymedon
And the chrysalis of the pale swallowtail. August 6, 2021.
Original description of Papilio eurymedon
Pierre-Hippolyte Lucas is credited with describing this butterfly. He published this description in the Revue et Magasin de Zoologie Pure et Appliquée in 1852. As with P. rutulus and several other California butterflies, Lucas first learned of this new swallowtail in a lecture by Boisduval on butterflies collected by Pierre Lorquin. Lucas then published this description, which appeared months before Boisduval's, and thus his name is forever associated with this butterfly.

©Dennis Walker