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Photo#31410
Black Swallowtail Pupae - Green and Brown Forms - Papilio polyxenes

Black Swallowtail Pupae - Green and Brown Forms - Papilio polyxenes
Fort Bragg, Cumberland County, North Carolina, USA
August 24, 2005

What is the cause of the color forms?
I have about 15 of these, and only 3 are green.

 
As far as I know
green occurs when they pupate on green twigs or vegetation, and brown on brown twigs. I don't know how they distinguish though, or what would happen in captivity with no vegetation present.

 
I think that Hannah's answer is pretty close,
but it's not quite that simple. Just based on what I've seen, I know they don't always get it right (at least not by those criteria). They also seem to be more often green under humid conditions, and those that overwinter are almost always brown or gray (or even a bit pinkish). I expect that there may be a genetic element too. Since some broods produce more brown, and some (from different mothers) produce more green, even when reared at the same time under the same conditions. In some regions they are almost never green, in others they often are. It's probably complicated and involves a combination of genetics and conditions encountered while the larva is growing and when it pupates. But - mostly they do end up matching their background (they may choose the background based on what color they are going to be too, as apposed to turning the color of the background - hard to say for sure).

 
I don't know.
If you find out please let me know.

Moved
Moved from Black Swallowtail.

Are these some of your 40 caterpillars from last month
that we discussed in forums? I've been wondering how many pupated, and have any emerged yet?

 
Yes,
see comments under .

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