BugInfo Monarch Butterflies

ORDER: Lepidoptera | FAMILY: Nymphalidae | GENUS: Danaus | SPECIES: plexippus

Status: Widespread common butterfly, best known as migrant.

Description: Monarch Butterflies have contrasting colors of black and orange, and are one of the most familiar of butterflies. Both sexes have the same appearance, and the wingspan is 3 to 4 inches. The well known caterpillars are banded with yellow, black, and cream. Tentacles are present at both ends of the body of the caterpillar.

Distribution: Monarchs are a primary example of true migration in insects. From their natural home in the Western Hemisphere, they have spread to Hawaii, Indonesia, the Canary Islands, and Australasia. They are also known from the Mediterranean. Normal migration patterns in the United States in the fall lead to northern Mexico and California.

Life cycle: For survival, the Monarch Butterfly requires only a warm climate and food plants (milkweeds for larvae, nectar from general flowers for adults). Several broods are produced throughout the year. After migrating and overwintering in the south (California and Mexico) , the adults travel north in the spring, laying eggs along the way. There is no swarming during the spring flight.

Migration. A serious attempt was begun in 1937 to determine where most Monarchs overwintered, when Fred Urquhart and his wife Norah released thousands of individual butterflies with paper tags glued to their wings, requesting finders of the insects to send them back to the Zoology Department at the University in Toronto, Canada.

Not until 1975 was an overwintering site found in Mexico by two collaborators of the Urquharts, Cathy and Ken Brugger of Mexico City. There are 12 known pockets of forests in Mexico where Monarchs gather for the winter. They have been seen in the Sierra Madre Mountains of Mexico by the tens of millions, and estimated at 4 million butterflies per acre. All wintering sites are about 9,000 feet in elevation, generally cold with frosts at times. The Mexican government set aside five of the sites as protected biosphere areas in 1986, but logging continues because much of the area is under private ownership. The majority of Monarchs from the east side of the Rocky Mountains overwinter in Mexico, but those from west of the Rockies overwinter in groves of Monterey pines or eucalyptus trees at sites along the California coast, from San Francisco to Los Angeles.

NewsletterMonarch Watch is published by Orley R. Taylor, Department of Entomology, University of Kansas, Lawrence, KS 66045. Monarch Watch is a collaborative network of students, teachers, volunteers, and researchers investigating aspects of the Monarch Butterfly migration phenomenon and its biology. The project is directed at the University of Kansas by Dr. Taylor. The goals of Monarch Watch are to further science education, particularly in primary and secondary schools, to promote conservation of Monarch Butterflies, and to involve thousands of students and adults in a cooperative study of the Monarchs' fall migration. School teachers are particularly invited to become involved to assist the project, and to receive teaching assistance. The worldwide website address for this organization is www.MonarchWatch.org.

Selected References:

Brower, L. P. 1995. "Understanding and misunderstanding the migration of the Monarch Butterfly (Nymphalidae) in North America: 1857-1995.Journal of the Lepidopterists Society 49(4): 304-385.

Urquhart, F. A. 1960. The Monarch Butterfly. University of Toronto Press, Toronto.

Urquhart, F. A. 1976. "Found at last: the monarch's winter home." National Geographic, 150: 160-173.

Zahl, P. A. 1963. "Mystery of the monarch butterfly." National Geographic, 123: 588-598.

Prepared by the Department of Systematic Biology, Entomology Section,
National Museum of Natural History, in cooperation with Public Inquiry Services, 
Smithsonian Institution

Information Sheet Number 99