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Photo#215458
Caterpillar Bird-dropping Mimic - Papilio rutulus

Caterpillar Bird-dropping Mimic - Papilio rutulus
5 mi. south of Port Angeles, ~2,000 ft. elevation, Clallam County, Washington, USA
August 18, 2008
Size: ~1.5 cm
Chewing on a Red Alder leaf.

Images of this individual: tag all
Caterpillar Bird-dropping Mimic - Papilio rutulus Caterpillar Bird-dropping Mimic - Papilio rutulus Caterpillar Bird-dropping Mimic - Papilio rutulus Caterpillar Bird-dropping Mimic - Papilio rutulus

Tentatively moved to Western Tiger,
due to food plant - I've found several references to Western Tigers using Alder, and none for Pale Tigers.
Moved from Papilio.

It's a Western or Pale Tiger Swallowtail,
but I don't know how to tell which. I think Alder favors Western, but I may be wrong.

It's a swallowtail
and I think it's in genus Papilio. I'm not sure how many species you have out there. Western Tiger Swallowtail seems a likely ID - very similar to our eastern ones (early instar - later ones do not look like bird droppings).

We have no early instar Western Tigers in the guide yet, so here's an Eastern Tiger for comparison:


 
Thanks
We have seen at least two in our yard, the Pale, Papilio eurymedon, and the Western Papilio rutulus, and I've photographed the Anise Papilio zelicaon, in the area.
Pyle, in The Butterflies of Cascadia, shows only those three on the Olympic Peninsula.
I didn't know about the wildly varying appearance of the early caterpillars compared to the later ones.