Known for their annual autumn mass migration, the Monarch butterflies travel in millions for up to 3,000 miles (4,828 kilometers). to reach Mexico from the South Canada and United States. They must travel before the winter sets in, or they will die before reaching warmer shores. Monarch butterfly belongs to family Nymphalidae and is also called Milkweed Butterfly because it lays its egg on the underside of the milkweed plant . The larvae feed exclusively upon the poisonous leaves of milkweed to become full grown caterpillars. That is why the adult butterflies too are poisonous and are avoided by most predators. Having a weapon like poison for self-defense, the Monarch butterfly does not have to resort to any camouflage or hiding. Rather, its wings are colored to advertise to the potential predators to stay away or get killed. Its bright orange wings with distinctive black veins and margins dotted with white spots are warning signals that the good-looking butterfly is actually foul-tasting and poisonous. No wonder the coloring and the markings are mimicked by some non-poisonous butterflies like the Viceroy Butterfly. Earlier, it was regarded as a case of Batesian mimicry, but since Viceroy is supposedly more unpalatable than Monarch, it has been revised to be a case of Müllerian mimicry.