At one time this butterfly was thought to mimic the poisonous monarch butterfly to protect itself from being eaten. Monarch caterpillars eating milkweed absorbed substances called glycosides that are not only distasteful, but harmful to the heart of predators eating them. The non-poisonous viceroy butterfly gained protection from predators by mimicking the monarch.
But in the 1990’s scientists conducted an experiment that proved that viceroy butterflies are not very palatable either. Viceroy butterflies are distasteful because these caterpillars eat – willows and poplars, two tree families that produce noxious chemicals to deter herbivores from eating these leaves. Viceroy caterpillars absorb salicylic acid from these trees that ultimately makes the viceroy butterfly bitter tasting.
These two butterfly species have co-evolved to mimic each other for protection from birds and other marauders. Their brightly orange colored wings warn predators to steer clear of them. Yet 15% of the wintering monarchs in Mexico are predated each year by two birds -the black-backed oriole and the black-headed grosbeak as well as the black-eared mouse. How these birds and mouse are able to eat monarchs without consequences is poorly understood.
Although this mimicry protects monarchs and viceroys from most vertebrate species (those with backbones), it does not thwart predation from wasps, spiders, bacteria and viruses. Such is the balance of nature!