You are what you eat certainly applies to the Monarch butterflies. They are distasteful to birds because of milkweed poison stored in the Monarch caterpillar stage. Their bright colors are warning colors to the poison they carry.
Male monarchs have darker veins on their wings, and the males have a spot in the center of each hindwing from which pheromones are released. Males are also slightly larger.
Monarch “butterflies fly to one of many overwintering sites. The generation that overwinters generally does not reproduce until it leaves the overwintering site sometime in February and March. It is thought that the overwinter population of those east of the Rockies may reach as far north as Texas and Oklahoma during the spring migration. It is the second, third and fourth generations that return to their northern locations in the United States and Canada in the spring. No one understands how they are able to return to the same overwintering spots over a gap of several generations is still a subject of research. The flight path and patterns to the overwintering sites seem to be inherited, based on a combination of circadian rhythm and the position of the sun in the sky.
Monarch butterflies are one of the few insects capable of making transatlantic crossings. They are becoming more common in Bermuda due to increased usage of milkweed as an ornamental plant in flower gardens. Monarch butterflies born in Bermuda remain year round due to the island’s mild climate.
A few monarchs turn up in the far southwest of Great Britain in years when the wind conditions are right, and have been sighted as far east as Long Bennington. Monarchs can also be found in New Zealand. On the islands of Hawaii no migrations have been noted.”
image and excerpts courtesy of wikipedia