The horn worm feed on tomatos, peppers and potatoes. they morph into very cool Sphinx moths some call hummingbird moths. Because I love my maters I dispatch them in soapy water. I saw two moths this week, so my dastardly deed did not rid me of them. Milkweed is the host to Monarch butterflies. You probably saw a hatching in progress. Best and Happy Yardening, Nancy.