"It’s not easy for tiny monarch caterpillars to eat milkweed leaves, with their sticky, toxic sap, but the caterpillars who survive become little packets of bitter poison. While the cardiac glycosides that monarch caterpillars glean from milkweed leaves do not make them completely immune to predation or parasitism, they are protected from all but the most well-adapted mouths," writes Emily Stone, Naturalist/Education Director at the Cable Natural History Museum.