First thing to do is plant it in the ground. It will overwinter better there. Where is your location? These native milkweeds, like speciosa, take a long time to establish. I have a few, 2 year old plants, that still haven't bloomed yet. I'm in Illinois, at the most eastern limit, of its range, and it was brought here from, further out west. I wouldn't panic about it spreading, and taking over. Instead, focus on caring for it, so it will establish. It may or may not bloom next year, ( depending on location), but be patient. These native species take longer to get established, but are well worth it. If your seedlings developed a large enough tuber, they should return, despite the caterpillar damage. I grow the, easy and fast growing Asclepias curassavica, and Gomphocarpus physocarpus, and I move any Monarch caterpillars that I find, on my native seedlings, to those tropical milkweeds.