When do they become pets?

Last year, I got a dill plant - and fairly well lost it to swallowtail caterpillars. Apparently, they like fennel and dill. So this year, I was going to get bronze fennel and dill, and transplant caterpillars from one to the other.

Then life intervened, and by the time I got to the greenhouse, all the fennel was long gone. So I got dill... and a packet of bronze fennel seeds were ordered.

It wasn't fast enough; the fennel is just putting out its first pair of true leaves, and the dill plant already has three caterpillars, hatched and hiding from the birds while munching down the herb. On the other hand, I'm not using a lot of dill, so I shrugged and ignored their existence.

Yesterday, there were only two left (probably bird), and I looked at the truly nasty weather incoming, thought for a minute, and then brought the pot inside, so they'd be safe. And then took pictures and showed them off to a friend. ((They're getting big. And are pretty!)

...at what point are the darned things pets?