These are so frequently mistaken as a Monarch but there are slight differences. The Monarch is a poisonous butterfly. Animals which eat a Monarch get very sick and vomit (but generally do not die). These animals remember that this brightly-colored butterfly made them very sick and will avoid all Monarchs in the future. For that reason, the very similar Viceroy is not bothered by such predators even though it is not poisonous.