The 'up' side to the butterfly caterpillars is that they are fairly predictable as far as what they will eat, aren't they Melanie? They don't just randomly chow down on everything. If you plant the right plants in a butterfly garden, they will have nectar plants and plants they will eat that you will expect to have eaten. You do have to interplant milkweed with some other plants, though, because once the monarch catts find it, it is just sticks and quite unsightly. But if you surround it with other nectar plants you can still keep your garden looking nice.
I have tons of butterflies, at least 6 or 7 different kinds, and other than the fennel, dill and parsley in my raised bed (which I now just plant extra plants of) they don't eat anything that I care about.
