found on orange tree - Papilio zelicaon

It is Papilio zelicaon

Both P. zelicaon and P. polyxenes will sometimes feed on plants in the Rue Family, including Citrus. Based on behavior of the "Zelicaon Group's" closest relations in Asia, this is probably an ancestral food plant for the group, but some time way back, an ancestor of most of the Zelicaon Group switched to Apiaceae as the favored family. [Some - the north American Papilio bairdii complex - have taken it a step further and feed on chemically similar species of Asteraceae (but these will still take Apiaceae and Rutaceae in a pinch too).] P. xuthus and P. polyxenes coloro are both in the Zelicaon Group, and both use Rutaceae (at least normally).

… David J. Ferguson, 8 July, 2009 - 6:49pm

Do you have the Great Swallowtail out there?

Feeding on orange is the delight of Papilio cresphontes!
The young caterpillars look different though

… john and jane balaban, 15 June, 2009 - 8:54pm

no oranges

the tree is rather young & there is no fruit on the tree. do you mean feeding on the trees themselves is a treat?

… Heather, 15 June, 2009 - 9:54pm

Yes, we meant the leaves

but now we think you're right and it's just a caterpillar on the wrong tree, not on its food plant.

… john and jane balaban, 15 June, 2009 - 10:09pm

another angle

I have a photo of this caterpillar from another angle but, still does not look like what you have posted. It is posted above

… Heather, 15 June, 2009 - 10:38pm

This looks like

the caterpillar of the Black Swallowtail Butterfly but it's on the wrong plant. These caterpillars eat parsley, wild carrot and related plants.
Compare with

… Marie L. Schmidt, 15 June, 2009 - 7:53pm

confused

I guess the caterpillar is confused. I do have carrots in my garden but, nowhere near this orange tree. There is alyssum & hummingbird vine growing at the bottom of this tree but, no carrots or parsley. The Queen Anne's Lace that's nearby is in the same class as carrot & parsley. Wonder if that is how it got there.

odd

… Heather, 15 June, 2009 - 7:58pm

Citrus is a host

Anise swallowtail larvae can feed on citrus.

http://en.wikipedia.org/wiki/Anise_Swallowtail

… R. Berg, 10 September, 2009 - 12:17am

The guide page for Black Swallowtail...

...does list Queen Anne's Lace as a food plant, so maybe you've found your answer. I'm curious if anyone else responding to this post can tell me how you distinguish the difference between the Black Swallowtail larva (already shown) and the Anise Swallowtail larva (below)?

… Harsi S. Parker, 16 June, 2009 - 12:30am

Queen Anne's Lace

is another name for Wild Carrot (Daucus carota). The Anis Swallowtail occurs only in the western part of North America. According to BugGuide the Black Swallowtail is found in the East and Midwest and its range overlaps only in California with the Anis Swallowtail.

… Marie L. Schmidt, 16 June, 2009 - 9:01am