Butterfly factory

I picked up a small purple fennel plant the other day and was amused to see two tiny black and white caterpillars on it. In fact, every fennel available at that garden centre had at least one resident caterpillar. In about a week, they've perhaps tripled in size and moulted into a different outfit. I'd been warned - or promised, depending on your viewpoint - that Foeniculum vulgare was a regular caterpillar factory for the black swallowtail, so that's what I'm hoping these little guys are. I'm going to let them stay, unless they threaten to obliterate the plant. Next time, if you're lucky, you might even get a picture of the plant!

I've had conflicting reports on its hardiness here, but if datura can come back... My Italian mother-in-law is a great fan of fennel seeds, so I should be able to impress her when I turn up with seeds in the fall.