Probably Two-Tailed Swallowtail Caterpillar

Subject: What type of swallowtail?
Location: Eagle Point, Oregon 9752r
August 18, 2016 3:19 pm
Hi, I just spotted this caterpillar this morning. I live in Eagle Point Oregon (southern oregon). I think it is maybe a western tiger swallowtail but am not sure due to the orange coloring.
Signature: Lara

Western Tiger Swallowtail Caterpillar
Possibly Two-Tailed Swallowtail Caterpillar

Dear Lara,
Based on the caterpillar’s appearance, and your location, the only other possible species are the Pale Tiger Swallowtail and the Two-Tailed Swallowtail, so we turned to BugGuide where the comparison between two are described as:  “Larvae very similar to those of Pale Tiger Swallowtail, but black pupil of false eye-spot larger, and yellow spot inside eyespot entirely separated from it, not just notched.”  You may visually compare the difference in the eyespots by comparing this BugGuide image of the Caterpillar of a Western Tiger Swallowtail with this BugGuide image of the Caterpillar of a Pale Tiger Swallowtail Caterpillar,
Papilio eurymedon.  Between the two, we are inclined to agree with you that this is the caterpillar of a Western Tiger Swallowtail, but we still haven’t considered the Two-Tailed Swallowtail.  The Two-Tailed Swallowtail Caterpillar is described on BugGuide as:  “Caterpillars resemble those of Eastern Tiger Swallowtail” which isn’t much help, nor is comparing your image to that of a Two-Tailed Swallowtail Caterpillar, Papilio multicaudatus, on BugGuide.  We have a very difficult time distinguishing between the species, so we are contacting Keith Wolfe for his opinion.  We are guessing it is a Two-Tailed Swallowtail Caterpillar based on image comparison of the eye spots.  One thing we can address is the orange color, which means your caterpillar is pre-pupal.  It has left its food source and is searching for a place to pupate.

Western Tiger Swallowtail Caterpillar
Possibly Two-Tailed Swallowtail Caterpillar

Keith Wolfe Responds
Hello Lara and Daniel,
Caterpillars of the Pale, Two-tailed, and Western swallowtails are indeed difficult to distinguish by appearance alone, thus their somewhat differing preference of Oregonian hostplants — or in this case, shrubs/trees growing nearby — is probably the best indicator . . .
* Pale Swallowtail (Papilio eurymedon): Mainly various wild lilacs (Ceanothus).
* Two-tailed Swallowtail (Papilio multicaudata): Mostly wild cherries (Prunus), ash (Fraxinus), and hoptree (Ptelea).
* Western Tiger Swallowtail (Papilio rutulus): Many species of aspen and poplar (Populus), willow (Salix), and maple (Acer).
Hopefully the above isn’t too “scientific”.
Best wishes,

Lara Responds
Thank you.  Nearby to where I found it are Ash and Oak trees primarily.

Ed. Note:  Based on the information provided by Keith Wolfe and the response from Lara, we can speculate this is most likely the caterpillar of a Two-Tailed Swallowtail.

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