Monarch butterflies use the Viceroy butterfly's resemblance to them for protection by avoiding predation, while the Viceroy gains protection by resembling the toxic Monarch. The Purple Coneflower or Echinacea plant is used by Monarch caterpillars as a food source and by humans to support the immune system. Willow trees contain salicylic acid which is similar to aspirin and helped humans with aches and pains for thousands of years through the process of character displacement between species.