Funny you should post this. A few weeks back I had some swallowtails that seemed to take a lot longer than normal. They finally pupated and eclosed just fine.

Maybe they're like people and some are just more pokey than others. :) Now, if it's a Giant Swallowtail, those do take longer than Black Swallowtails. I think there are variations in caterpillars and some are faster than others at pupating.
Cathy

I collected 4 Black Swallowtail eggs about 2 weeks ago - they were all laid at the same time on some Rue and Parlsey that has gone to seed. I was out in the garden and WATCHED the female lay the eggs, and that is probably the only reason I found them, otherwise it seems near impossible to find the eggs or small cats.

I kid you not, all four cats are growing in the same container and they are 4 different sizes. The two growing on the Rue clippings are growing more slowly than the 2 on parsley seedheads. One is actually pupating today - another still looks like 2nd instar! Weird!

Are some sickly? Could host plants make a difference how fast they grow? These cats preferred to stay on the host plant on which they were laid although they had access to the other. Or maybe, could this be a natural survival mechanism to space out the flight time of the species? I have no idea. We'll see if they all pupate okay.

Thanks everybody, I guess I'll just wait. We have had so many Giant Swallowtails around our Butterfly Bush. I assume this is a Black Swallowtail since it looks like the one I had last year. Do the Black and Giant Swallowtail cats look different?
Yesterday I found a Monarch cat and another swallowtail cat. Today I found 2 swallowtail eggs. Let's see how many make it!

Yes, Black Swallowtail and Giant Swallowtail larvae look TOTALLY different! The Giant larvae look like bird poop. The Black ST starts off black and white and then changes to green! The swallowtails DO take longer, sometimes, and they vary so much from caterpillar to caterpillar. I have two Anise Swallowtails that have been in diapause for a year. ;P Yes, they are still alive, and yes, I have had beautiful adults eclose after over two years, even! So, hang in there. As for food and differences in growth, I don't know if there is anything there as I mix up the foods (Rue and assorted orange leaves for the Giant, for example). I prefer the 'salad' approach to feeding.

Here is a link that might be useful: My Butterfly Guide's Anise Swallowtail page