The best known and one of the most colorful butterflies in the Americas is the Monarch Butterfly. The larvae or caterpillars of this species feed primarily on various species of milkweeds, and it is from these milkweed leaves that they accumulate strong poisons called cardenolids. A close relative of the Monarch is the more southern species, Queen. Queen caterpillars also eat milkweeds, and the poisons they accumulate, as in Monarchs, remain in the bodies of the adults. A bird, after eating the foul tasting and poisonous Monarch learns to leave it alone the next time it hunts for food. An unrelated butterfly, but one that looks similar to a Monarch, is the less common Viceroy. Because Viceroys mimic Monarchs, Viceroys are not taken by birds who have taken a bite of a poisonous and foul-tasting Monarch. This type of mimicry where an unrelated, non-poisonous species mimics a more common poisonous species is called Batesian mimicry. Experiments have shown that Monarchs are much more poisonous than their close relative Queens even though Queens also eat milkweeds. When a mostly non-poisonous related species, Queen, is not eaten by a predator who has consumed a Monarch, this type of mimicry is called Müllerian mimicry.
Often overlooked are flies that mimic bees. Four of the many examples are the drone fly (Eristalis tenax), the bee fly (Exoprosopa sp.) the flower fly (Chrysotoxum sp.) and the very cool robber fly (Laphria sp.) which resembles a bumble bee. Flies can be separated from bees by looking at the shorter antennae in flies, plus flies have one set of wings while bees have two sets. For comparison here is a leaf-cutter bee (Megachile sp.) and an attractive sweat bee (Agapostemon sp.).