Perennial plants in the genus Asclepias (milkweeds) contain compounds called cardiac glucosides (cardenolides) that can be toxic for animals. Monarch butterfly larvae feed on Asciepias sp. but are not harmed by the cardenolides. Instead these molecules accumulate in the tissues of the caterpillar and are present in the tissues of the adult butterfly. Because of these toxins in their tissues, Monarch butterflies are unpalatable to insectivorous birds. Another species of butterfly, the Viceroy, looks very similar to the Monarch in its bright coloration and distinctive patterning but was thought to lack a toxin. Because Monarch butterflies are toxic it was long thought that the similar appearance of nontoxic Viceroy butterflies was an example of: