Awaiting Papilio rutulus or Papilio multicaudata?
Sat, Apr 11, 2009 at 7:14 PM
I tried sending these through the website but it kept failing. Hope this is OK.
We here in Montana have been long awaiting the arrival of some overwintering Papilio/Swallowtails in our garage. Try as we might, we have not been able to determine if our caterpillars were Two-tailed or Western Tiger Swallowtails. The difference will determine if they should emerge in late May or late June (around here.) We have been waiting so patiently, it would be such a shame for us to mess up the timing now. (The garage stays so cold we will probably have to move them to get them to emerge.) We have some great photos of several different caterpillar stages as well as the pupae. Attached are a few. These caterpillars fed on chokecherry leaves in late summer (found them August 20th) and pupated mid-September. The early instars were green and had a bird (swallow?) like pattern across their backs.

Swallowtail Caterpillar

As they grew, the bird pattern faded. When they reached about two inches in length they turned brown, stopped eating and became very active. Then they hung themselves horizontally from a piece of silk (appearantly called a girdle) which you can see in the photo. Then they pupated and we have been waiting ever since. We are very excited that spring is approaching here in Big Sky, Montana (although we still have quite a while to wait.) We will send photos of the adults when they emerge. It will be interesting to see which species of swallowtail they are; it is also possible they are Canadian Swallowtails. Also, we wonder if it is possible to determine the gender? Thanks for listening.
Bigskybugkids

Swallowtail Caterpillar

Dear Bigskybugkids,
This presents an interesting identification challenge. There is an image on BugGuide of a Canadian Swallowtail Caterpillar, Papilio canadensis, that illustrates the “swallow-like” markings, but it also has distinctive horns at the end of the abdominal section. Cherry is listed as a larval food on BugGuide as well. Chokecherry is specifically listed as a larval food of the Two Tailed Swallowtail Caterpillar, Papilio multicaudata, on BugGuide. With regards to the Western Tiger Swallowtail Caterpillar, BugGuide indicates: “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.” Those two characteristics are present in your specimen, but neither cherry nor chokecherry are listed as food plants for the larvae. The images of the Two Tailed Swallowtail Caterpillars on BugGuide show a similar pupil-less eyespot and separated yellow spot, virtually identical to the Western Tiger Swallowtail. Based on the eyespot match and the food plant match, we would suspect the Two Tailed Swallowtail to be the frontrunner. Guess the adult images will have to be the final determination. We suspect DNA may be required to determine the sex of a caterpillar.

Swallowtail Chrysalis

Update:
Awaiting Papilio rutulus or Papilio multicaudata?)
Fri, Jun 12, 2009 at 3:42 PM
After a refreshing 10 month nap…the swallowtails have emerged. It looks like they are Two-Tailed: you were so right. The tell-tale (tail ) sign was the _/*thinly*/_ ringed blue/green spot inside the yellow eye spots…the Western looks almost the same but the ring is thicker. Thanks again…and, no, we still can’t tell the boy butterflies from the girls.
(ed. note: We believe this would be from Montana)

Two Tailed Swallowtail

Dear bigskybugkids,
Thanks so much for sending us the photos of your newly emerged Two Tailed Swallowtails. We will be posting them today as their own posting as well as an update to the caterpillar photos you sent in April.

Two Tailed Swallowtail