Müllerian mimic. Müllerian mimicry is when two or more harmful species, that may or may not be closely related and share one or more common predators, have come to mimic each other's warning signals.
The Viceroy caterpillars feed on trees in the willow family (Salicaceae), including willows (Salix), and poplars and cottonwoods (Populus). The caterpillars sequester the salicylic acid from these trees, in their bodies, which makes them bitter, and upsets predators' stomachs.
The Viceroy butterfly nectars on flowers. They also can be found puddling and feeding on aphid honeydew, carrion, decaying fungi, dung, rotting fruit, and tree sap.