Interesting...yes the scarlett milkweed has had a problem for ants here in my little patio garden. I usually watch where they go to see if there are aphids. Well, I've gotten rid of the aphids and the ants are still busy as ever. Turns out that the scarlett's flower is rather sweet.
I don't know if it's just something it does naturally, or if it's because I spray mist water on them, but a little droplet collects on the top of the flowers, and I've tasted it and it is MIGHTY SWEET. Then I saw the ants there at the flower tops, so I'm fairly sure that's what they're interested in now.
How can I keep ants off the plants without disturbing the plants and thus the cats/butterflies? NOTE: they are all on a patio in pots.