Black Swallowtail caterpillars (question, no pics)

[CaraRose]

Well, I noticed two caterpillars (looks to me like black swallowtail first instars) on my fennel plants. I don't want to hurt them (I'm growing the fennel for the bulbs, so I don't mind sharing the fronds), but I also noticed aphids and dairy ants. I want to spray for the aphids before they do too much damage, without hurting the caterpillars.

I also have a growbag of carrots. Does anyone know if they eat carrot greens as well? I'd like to transfer them over so I can spray the fennel and take care of the aphids.

Going to try and get some shots of the caterpillars tomorrow if I can find them.

[SmartWombat]

Caterpillars are usually very specific on their food plant, and even another in the same family won't do for some species.
I'd give you odds of 50-50 for them surviving to pupate if there are ichneumon wasps about to parasitise them. Plus birds would probably like them too.
I'd just enjoy them while I can. And get good macro shots of the ants "milking" the aphids for sugar.

I don't know if they're a species that wanders off the food plant to pupate, or if their entire lifecycle is around the one plant. A possibility (I used to do this with other species) is to uproot the fennel, remove the ants, replant it in a pot and grow it indoors, and remove the aphids by hand.

Admittedly my experience was with Tortoiseshell butterfly and Emperor moth, where I gathered dozens of caterpillars in their gregarious phase but I had about 90% success rate to pupation.

[CaraRose]

Thanks Paul.

I also need to thin the fennel down (the container I'm growing them in can hold 3-4 adult plants, I have about 20 of the young plants in there right now). Maybe I'll attempt to transplant a few of the plants I'm thinning to a separate pot and move the caterpillars to them. I don't know how well fennel transplants though.