Butterfly Milkweed (Asclepias tuberosa) Found throughout the U.S.
This favorite of the monarch butterfly is actually fighting an evolutionary war. Butterfly milkweed is full of toxins, which monarch larvae ingest and absorb in order to become poisonous themselves. But the milkweed doesn’t want to be eaten — so it secretes a thick latex that gums up the mouthparts of the larvae. Not to be outdone, the larvae cut notches in the leaves to slow the flow of latex while they eat. The result? A delicate balance that allows both to survive. (Thanks to Andrea DeLong-Amaya/Lady Bird Johnson Wildflower Center and Kris Light/East Tennessee Wildflowers, for their help.)