It's a magnificent swallowtail/papilio garamas. I looked up the host plant, and it's listed as avacado, which is a type of persea, which is what our palamedes swallowtails use, mainly p. borbonia and p. palustris. So that explains why it looks a lot like a palamedes swallowtail - it's closely related.
Sherry

Sherry,
Thanks so much for the quick response! My friend will be so happy for this ID. I'll tell her that you provided her with the ID on it.
Cathy

Tell your friend that it was a great opportunity to see and get pictures of this species. They are a high flying species that only ocassionally comes down out of the forest canopy to nectar or sip mud. P. g. syedra is the ssp I mostly came across when I was heavily working on the Memphis species (Charaxinae, and another genus of canopy dwellers) in Central America. They very rarely get within 50-75 feet of the ground.

Absolutely beautiful butterfly.

That is a very Tropical butterfly! There is only one U.S record of that butterfly. It was in the 1960s after a hurricane. It was found in the Rio Grande Valley where I live. :-)

Larry, I very much appreciate your expert information about this butterfly, and I will be sure to tell my friend. She was excited to see it, and now I know that it will have even more meaning to her after she knows what you said here. It think it would be wonderful to be able to study all of the butterflies that you have over the years and to be able to share your experience with others.

Sandy, Yes, I thought so too and so did my friend when she saw it. She was actually in Mexico to see the Monarchs before they started their journey northward. I hear now that they're getting to be on their way.

Danny, I looked on the butterfliesandmoths.org website and saw that it was only reported in the southernmost county in Texas. I guess it was blown pretty far north of its regular stomping grounds then from the hurricane. You'll have to keep your eyes open and maybe you'll see one too someday. ;-)

Cathy

I was very surprised to see this butterfly here, but then was not surprised when I read the message more closely and saw that it was in Mexico. I saw a lot of these last summer in Michoacan, but I never got close enough to get a picture as good as yours. They really live up to their name -- they are truly magnificent.
{{gwi:458221}} {{gwi:458223}}
geni

Geni, I thought that you might have seen some down there already since you spend so much time in Mexico. It's nice that you got to see so many. Your pictures of them on the zinnias are very pretty! Thank you for your comments, and I will tell my friend what you said. Actually, I think I'll give her the link to this page and she can see what you all said. She and I actually met on a birding forum and have met in person. It's just within the past few years that we've both gotten into butterflies and enjoy them very much. I know that Barb will like reading what you've had to say.
Cathy