Monarch butterfly (Danaus plexippus) is a well-known North American butterfly. Since the 19th century, it is also found in New Zealand, and in Australia where it is also known as the Wanderer Butterfly. In Europe it is resident in the Canary Islands and Madeira, and is found as a migrant in Mexico, Azores, Portugal and Spain. Its wings feature an easily recognizable orange and black pattern, with a wingspan of 8.5–12.5 cm (3.34 in–4.92in). (The Viceroy Butterfly has a similar size, color, and pattern, but can be distinguished by an extra black stripe across the hindwing.) Female monarchs have darker veins on their wings, and the males have a spot in the center of each hindwing from which pheromones are released.
Monarchs are especially noted for their lengthy annual migration. They make massive southward migrations starting in August until the first frost. A northward migration takes place in the spring. Female Monarchs deposit eggs for the next generation during these migrations. By the end of October, the population of the Rocky Mountains migrates to the sanctuaries in the area of Angangueo, Ocampo, Zitácuaro and El Rosario in Michoacán, Mexico. The western population overwinters in various sites in central coastal California, United States, notably in Pacific Grove and Santa Cruz. The length of these journeys exceeds the normal lifespan of most Monarchs, which is less than two months for butterflies born in early summer. The last generation of the summer enters into a non-reproductive phase known as diapause and may live up to 7 months.
During diapause, 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 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. How the species manages to return to the same overwintering spots over a gap of several generations is still a subject of research; the flight patterns appear 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.