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Photo taken in Lenfestey Family Courtyard

monarch butterfly.

Monarch Butterfly (Danaus plexippus)

As the first frosts occur during October, the last of the monarch butterflies (Danaus plexippus) finally depart northeastern Wisconsin. This familiar butterfly is one of the most remarkable migratory animals in the world. Individuals tagged by Dr. Fred Urquhart of the University of Toronto during the 1970's led to the discovery that adult monarchs from northern U.S. and southern Canada migrate south as far as Mexico. We now know that the entire eastern North American population overwinters in about 30 sites west of Mexico City (Layberry et al. 1998). Unfortunately, an ice-storm in 2001 killed a large number of overwintering monarchs. Habitat destruction and herbicide use throughout the range of these butterflies also threatens this species.

Most of Wisconsin's monarchs fail to reach the Mexican wintering areas, although a few individuals successfully make the long journey. In early spring, most of the overwintering monarchs reproduce in Mexico or the Gulf States and their offspring move northward. Monarchs reaching our area are second or third generation descendents of the original overwintering butterflies. Studies by Malcom et al. (1993) showed that more than 90% of the monarchs in the northern U.S. during June are descended from butterflies that reproduced earlier that year in Mexico or the Gulf States.

Monarch caterpillars feed on milkweeds in the genus Asclepias. These plants contain toxic cardiac glycosides that protect them from many herbivores. However, the monarch larvae are unaffected by these poisons, but they render the larva and adults distasteful and cause vomiting in certain predators such as birds. Classic studies by Brower (1958) have shown that birds like Blue Jays learn to recognize the color pattern of monarchs and avoid them. Monarchs advertise their toxicity with bright orange and black warning (aposematic) coloration. Other species of butterflies, such as the Viceroy, Limenitis archippus have a very similar color pattern and are also avoided by birds. Rollover the monarch image above to observe the similarity between the monarch and the viceroy.

Viceroys and Monarchs are currently thought to exhibit Mullerian mimicry. Mullerian mimicry occurs when toxic species resemble other toxic species, often by sharing aposematic colorations and patterns. The yellow and black stripes on bees and wasps are a classic example. Predators learn to avoid species that have similar warning coloration. The bright orange and black pattern on the monarch and the viceroy is aposematic: a warning to predators that they are toxic species. The similarity in the pattern between the 2 species reinforces the warning to potential predators. Mimicry also occurs where an edible species closely resembles a toxic species to fool potential predators into believing it is also toxic and should be avoided. This type of mimicry is called Batesian mimicry. Viceroys were once thought to be edible Batesian mimics of monarchs, but recent research has shown that viceroys also produce toxins to deter bird predators.


Brower, J.V.Z. 1958. Experimental studies of mimicry in some North American butterflies. Part 1. The monarch, Danaus plexipus, and the viceroy, Limenitis archippus archippus. Evolution.12:32-47.

Layberry, R.A., P.W. Hall, and J.D. LaFontaine. 1998. The butterflies of Canada. University of Toronto Press. Toronto.

Malcom, S.B., B.J. Cockerel, and L.P. Brower. 1993. Spring recolonization of eastern North America by the monarch butterfly: successive brood or single sweep migration? In S.B. Malcom and M.P. Zalucki, eds. Biology and conservation of the monarch butterfly, 253-67. Publications of the Natural History Museum of Los Angeles County. Los Angeles.

Ritland, David B. and Brower, Lincoln P. "The Viceroy is not a Batesian Mimic". Nature. Vol.350, 1991.p. 497-498



Text and photos contributed by UW Green Bay professor Bob Howe

© 2001-2004 The Cofrin Center for Biodiversity and the University of Wisconsin Green Bay, All Rights Reserved
Last updated on May 12, 2014