Those aren't swallowtail cats, Jo. Black swallowtails, which are the ones that use dill, are dark brown with a white 'saddle' in their early instars, then they molt into an orange, white and yellow instar, with them being a beautiful green, yellow and white in the final instar.
I don't know what your cats are, probably a moth, maybe sawflies.
Sherry

Thanks Misssherry.
Just realized (after google search) that they weren't swallowtails. I have so many flying around, I just assumed they were swallowtails.
Well, just looked again and they are gone!! Guess it was a hungry bird!
If they were moths, glad they are gone-although now...so is my dill!!
Keep wondering if those gross hornworms will soon be eating my tomatoes.
Wish I could get some butterfly cats!!
I have the habitat, the host plants and the adult butterflies.
I'll keep looking!
Jo

You know what...I think these were some kind of butterfly.
When you said saddle- I found a pic that looked similar.
When I said it had a stripe down the middle, I meant across the middle of the body-not lengthwise.
This pic was a black swallowtail-1st instar.
Anyway, where did these cats go? Do birds eat them?
I am sick that they are gone and that they WERE butterfly cats.
I took a very blurry pic, but will post it anyway.
{{gwi:500979}}

It does look like a black swallowtail - I've never seen one that could ever be described as yellow, so I didn't think that was what you had.
I'm sorry your cats disappeared. They were probably eaten by wasps or stinkbugs - that's why we raise ours in cages and release them as adults.
Here's an early instar cat, though not a hatchling -
{{gwi:491334}}
And here's a later instar-
{{gwi:452408}}
And here's two last instar cats - the green one is the regular color, the other is the dark form -
{{gwi:491338}}
Sherry