Clouded Sulphurs nectar at flowers such as Milkweed (Asclepias sp.), Butterfly Bush (Buddleja sp.), Coneflower (Dracopis, Echinacea, and Rudbeckia), Alfalfa (Medicago sativa), Dandelion (Taraxacum sp.), Clover (Trifolium sp.), and Tall verbena (Verbena bonariensis) and many more.
The name was given by Carolus Linnaeus in honor of his teacher at Uppsala University, Professor Olof Rudbeck the Younger (1660-1740), and his father, Professor Olof Rudbeck the Elder (1630-1702), both of whom were botanists.