Thursday, June 11, 2009


Nature Watch

By Susan Benson,
CNHM Director of Education

Monarch butterflies are friendly visitors to northwest Wisconsin. In fact, there aren’t many places on this continent that Monarchs aren’t found this time of year.

This butterfly’s range covers the same ground as does the milkweed plant. That is no coincidence, as the milkweed is the Monarch’s primary source of food. This plant provides the butterflies with nutrition, but something else too. Milkweed produces poisonous chemicals called cardiac glycosides. In humans, these chemicals increase the force of contraction of the heart. Monarchs have adapted to the plant’s effects, so a meal of milkweed doesn’t affect them. However, after eating milkweed, the Monarch itself becomes poisonous—an intriguing form of chemical protection. The beautiful orange color of the Monarch butterfly warns its predators that their intended meal might be toxic.

During the summer, female Monarchs each lay about 400 eggs on the underside of leaves of milkweed plants. The eggs develop for about two weeks, slowly changing color from yellow to light gray. Eventually the caterpillar’s head becomes is visible through its eggshell. At hatching, a caterpillar’s head is larger than the rest of its body; with its jaws, the caterpillar cuts through the egg and waves its head and body to break free.

On the first day of life, the caterpillar consumes its own weight in food, and its first meal is the eggshell. Over the next few days, the caterpillar eats day and night, only stopping to rest between meals. Fully developed, the caterpillar is about two inches long and weighs 2,700 times more than when it hatched.

After two weeks, the caterpillar comes to rest and starts to form a chrysalis. This stage in the insect’s life is the most amazing. Inside the chrysalis, the caterpillar forms wings, the body changes from worm-like to insect-like, and the brilliant orange color of the wings is created.

As adults, Monarch butterflies are migratory creatures. They travel great distances each fall to spend winter in temperate climates. Despite the fact that the range of the Monarch’s summer home is quite expansive, the wintering grounds are very limited. Some of these butterflies travel more than 2,900 kilometers to spend winter in places such as Michoacan, Mexico. Other Monarchs overwinter in Cuba, and Pacific Grove, as well as Newark, California.

Saturday, May 23 was the first time I saw a monarch this season. Other common butterflies that can be observed right now include the yellow tiger swallowtail and the tiny blue butterfly called the spring blue. Keep your eyes out for these adult beauties. Or, if you see milkweed plants, try turning over a few leaves for their light green monarch eggs.

Nature Watch is brought to you by the Cable Natural History Museum. For 40 years, the Museum has served as a guide and mentor to generations of visitors and residents interested in learning to better appreciate and care for the extraordinary natural resources of the region. The Museum invites you to visit its facility and exhibits, the Curiosity Center and Brain Teasers 2, in Cable at 13470 County Highway M. Also find us on the web at to learn more about exhibits and programs.

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