We decided to collect seed from this very common grass weed so that we could intentionally plant it in areas that would be better suited to raise caterpillars. The ones in our yard tend to grow in the driveway.
Though we offer the American Lady butterfly plenty of host plant choices in our habitat, they consistently choose cudweed as a host.
If you are concerned about it spreading out of control, consider growing it in a pot where you can keep track of it and remove the flower heads before they go to seed.
You’ll know if you have caterpillars when you see the leaf nests at the top of the plant. It seems once the caterpillar reaches a certain size it stops making the nest. Chrysalis colors are either white or yellow.