Monarch Butterflies (Danaus plexippus) and Butterfly Weed (Asclepias tuberosa) Monarch Butterflies and Butterfly Weed, a type of milkweed, have coevolved as plant and pollinator. This means that they both rely on one another to survive. Milkweed is the primary source of nutrition for monarchs. Monarchs only eat Asclepias tuberosa a particular species of Milkweed. The monarch relies on toxins in the milkweed to fend off predators such as birds. The toxic tendencies of the milkweed plants caused the government to attempt o eradicated the plant along roadsides and in cow pastures. This h