Published on July 12, 2016
The monarch butterfly or simply monarch (Danaus plexippus) is a milkweed butterfly (subfamily Danainae) in the family Nymphalidae. Other common names depending on region include milkweed, common tiger, wanderer, and black veined brown. It may be the most familiar North American butterfly, and is considered an iconic pollinator species. Its wings feature an easily recognizable black, orange, and white pattern, with a wingspan of 8.9–10.2 cm (3½–4 in) The viceroy butterfly is similar in color and pattern, but is markedly smaller and has an extra black stripe across each hind wing.
The eastern North American monarch population is notable for its annual southward late-summer/autumn migration from the United States and southern Canada to Mexico. During the fall migration, monarchs cover thousands of miles, with a corresponding multi-generational return north. The western North American population of monarchs west of the Rocky Mountains often migrates to sites in California but has been found in overwintering Mexican sites as well. Monarchs were transported to the International Space Station and were bred there.
After a ten-fold drop in the population of the eastern monarch butterfly population over the last decade, a 2016 study predicted an 11%–57% probability that this population will go quasi-extinct over the next 20 years.
Commonly and easily mistaken for the similar viceroy butterfly, the monarch’s wingspan ranges from 8.9 to 10.2 centimetres (3.5–4.0 in). The upper sides of the wings are tawny-orange, the veins and margins are black, and in the margins are two series of small white spots. Monarch forewings also have a few orange spots near their tips. Wing undersides are similar, but the tips of forewings and hindwings are yellow-brown instead of tawny-orange and the white spots are larger. The shape and color of the wings change at the beginning of the migration and appear redder and more elongated than later migrants. Wings size and shape differ between migratory and non-migratory monarchs. Monarchs from eastern North America have larger and more angular forewings than those in the western population.
Monarch flight has been described as “slow and sailing”.
Adults exhibit sexual dimorphism. Males are slightly larger than females and have a black patch or spot of androconial scales on each hindwing (in some butterflies, these patches disperse pheromones, but are not known to do so in monarchs). The male’s black veins on his wings are lighter and narrower than those of females.
One variation, the “white monarch”, observed in Australia, New Zealand, Indonesia and the United States, is called nivosus by lepidopterists. It is grayish-white in all areas of its wings that are normally orange and is only about 1% or less of all monarchs, but populations as high as 10% exist on Oahu in Hawaii.
The monarch has six legs like all insects, but uses only its middle legs and hindlegs as the forelegs are vestigial, as in all other Nymphalidae, and held against its body.
The range of the western and eastern populations of the monarch butterfly expands and contracts depending upon the season. The range differs between breeding areas, migration routes, and winter roosts. However, no genetic differences between the western and eastern monarch populations exist; reproductive isolation has not led to subspeciation of these populations, as it has elsewhere within the species’ range.
In North America, the monarch ranges from southern Canada through northern South America. It has also been found in Bermuda, Cook Islands, Hawaii, Cuba and other Caribbean islands:(p18) the Solomons, New Caledonia, New Zealand, Papua New Guinea, Australia, the Azores, the Canary Islands, Gibraltar, Philippines, and North Africa. It appears in the UK in some years as an accidental migrant.
The monarch butterfly is not currently listed under the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES) or protected specifically under U.S. domestic laws. On 14 August 2014, the Center for Biological Diversity and the Center for Food Safety filed a legal petition requesting Endangered Species Act protection for the monarch and its habitat. The U.S. Fish and Wildlife Service initiated a Status Review of the Monarch Butterfly under the Endangered Species Act with a due date for information submission of 3 March 2015.
The monarch butterfly is listed as a Species of Special Concern in Ontario.
Monarch (Danaus plexippus), Central Park, New York, USA.
Overwintering populations of D. plexippus are found in Mexico, California, along the Gulf coast, year-round in Florida, and in Arizona where the habitat has the specific conditions necessary for their survival. Their overwintering habitat typically provides access to streams, plenty of sunlight (enabling body temperatures that allow flight), and appropriate roosting vegetation, and is relatively free of predators. Overwintering, roosting butterflies have been seen on basswoods, elms, sumacs, locusts, oaks, osage-oranges, mulberries, pecans, willows, cottonwoods, and mesquites. While breeding, monarch habitats can be found in agricultural fields, pasture land, prairie remnants, urban and suburban residential areas, gardens, trees, and roadsides – anywhere where there is access to larval host plants. Habitat restoration is a primary goal in monarch conservation efforts. Habitat requirements change during migration. During the fall migration, butterflies must have access to nectar-producing plants. During the spring migration, butterflies must have access to larval food plants and nectar plants.