New research has shown that monarch butterflies use medicinal plants, including species of milkweed plants, to treat offspring for diseases even before they hatch. Some of the milkweed plants the monarch caterpillars feed on produce chardenolides within the systems of the insects. These chemicals are harmless to the monarch's themselves but toxic to predators even once the monarch's become adults. Parasites that can invade Monarch caterpillars can stay with the insects even into adulthood and can be passed from infected females to her offspring.
Researchers at Emory University in Atlanta conducted experiments with monarch caterpillars feeding some on milkweed. Those exposed to the milkweed had fewer parasite infections and disease. Researchers also conducted experiments with parasite-infected and uninfected females who had access to milkweed and tropical milkweed. The infected females laid more eggs on the tropical milkweed (the medicinal plant) while uninfected females gave no preference.
Researchers next plan to work with a wider variety of milkweed and butterflies to expand their studies.
For more information on this fascinating way nature takes care of itself, you can read the MSNBC Technology and Science Article.