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BST; color variations

Posted by tracey_nj6 6 (My Page) on
Thu, Sep 23, 10 at 16:56

What's the deal with the color variations between my 3 cats? I know it's nothing to be alarmed about, but I have never seen such a difference all at the same time. I currently have 7,
5 of which should be pupating very soon. I have 2 that are very dark. They're all eating the same plant.

Follow-Up Postings:

RE: BST; color variations

Have you had cool weather? The only time I notice that much black is when the weather is cool, with monarchs too. Wearing black in cool weather keeps you warmer when the sun is out. Just my theory. Nice photos.

RE: BST; color variations

Aren't they just gorgeous? I think that this is one of the prettiest cats. I have never had one of the black ones. Very cool!! I've had lots of variations in color of the pupa in relation to the color of the object that they pupate one. That is cool too.

RE: BST; color variations

I had more of the dark cats in my last black swallowtail batch than the normal colored ones, and this happened during the hottest part of summer. Those cats ate mock-bishop's weed, so I thought it might be the food, which is different from the usual rue or fennel.
They're really beautiful, though!
Image hosted by

RE: BST; color variations

The studies I've read on larval polyphenism suggest that larval color variances are probably the product of body temperature during certain periods of larval development (an environmental stimulus due to either or both ambient temperature and photoperiod/exposeure to the sun). But they can also be a product of hereditary genome. Set larval seasonal variations would make sense with the first suggested cause.

Hereditary genome is probably more logical for your mid summer dark brood Sherry (on the surface anyway). But its also thought that some temperate species (including P. polyxenes) have evolved their seasonal polyphenism to compensate for variations in body temperature caused by environmental influence. If that's true with this species then they would have no need for seasonal variations, so you decide.

In the case of Tracey's brood pictured above, with so much variation in larval color, hereditary genome is the logical choice (note that I said logical, not for sure). LOL

Adult altitudal polyphenism is common in some species for similar reasons.


RE: BST; color variations

Very interesting Larry; thanks for that info.
It's funny how much larger those black cats are. My two are huge, definitely the biggest I'd ever seen. They still haven't pupated yet, but 3 of the "normal" ones have, and they were much smaller.

RE: BST; color variations

My three black swallowtails that are now chrysalids were the same way. I found all three at the same time on my bronze fennel. They were all at 1st instar, the same size, identical looking, and the only cats on the plant at that time. I brought them in to raise and when they started to grow, they had three totally different patterns just like yours. Even the shade of green was a little different on them. They looked so different to me that I actually had to do some googling to see if there was another similar species that feed on fennel. Now their chrysalids are also three different shades. One is green, one is light brown, and one is a darker mottled brown. It will be interesting to see what the adults will look like. I just hope I don't have to wait until next year for them to eclose!

RE: BST; color variations

The larval size of your "black" cats is a product of their color. Black absorbes radiant heat and raises body temperature, allowing those cats to process resources more efficiently. Normally that suggests they would also complete their larval life cycle sooner than the "green" cats though.

Pupal color would not have any bearing on the appearance of the adults. But larval size attained because of larval color could effect the size of the adult.

And as Sherry touched on, larval food plant choice could also have bearing on larval size. Some plant species offer better resources than others. Also how well cats tolerate plant toxins could depend on the species of plant and where it grows, and that could effect larval size.

RE: BST; color variations

Sigh; one of the dark ones was found dead on the soil. Other one appears to be in pupation mode.

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