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Monarch Life Cycle and Natural History

The monarch butterfly is found throughout North America, from Canada south to South America and the Caribbean, and may be the most widely recognized of all American butterflies with its distinct orange, black, and white wings. The black border around its wings, rimmed with white spots makes them look like stained glass windows! When opened, its wings can reach as wide as four inches. You can tell the male monarch from the female by the two black spots on his hind wings and the thinner black webbing within. The female’s webbing is thicker and she lacks the distinctive wing spot.

Monarchs live mainly in prairies, meadows, roadsides, and grasslands. As caterpillars, they feed exclusively on milkweed, which makes the monarch toxic to predators such as birds. The monarch’s survival depends on this chemical defense. Adults are generalists and feed on a variety of blooming plants (containing great amounts of sugar). Adult monarchs are seen flying in Nebraska from June through the fall, so having plants that bloom throughout the summer and fall are needed for the adults to thrive.

Monarch butterfly reproduction is a complicated process. One female monarch can lay upwards of 400 eggs. The eggs are deposited on the underside of milkweed leaves and will hatch in as little as three days, depending on the temperature. The caterpillars, or larvae, feed on milkweed leaves for about two weeks, and grow from two mm to five cm long and molt (shed) up to four times. The caterpillars then attach themselves to a twig and shed their outer skin into a chrysalis, or pupa. This can happen within just a few hours! Packed tightly inside, the caterpillars will undergo the transformation into an adult butterfly in about two weeks. The entire life cycle from egg to adult is complete in about a month. In Nebraska, several generations of monarchs are born every summer.

The adult monarch butterfly typically only lives for a few weeks, unless it is lucky enough to be the last generation born in late August. The last generation is the migratory generation and can live eight or nine months. They delay reproduction and migrate south since monarchs cannot survive Midwest winters. These migratory monarchs must make the 3,000 mile journey to their overwintering grounds in Mexico. Scientists believe that monarchs use the position of the sun to let them know to begin their migration south. They also believe that the earth’s magnetic field helps them to figure out where to go. They need a lot of energy to make this trip each year. They store fat, gathered from the nectar of late summer blooming plants, which helps them make the long trip south. In the spring, those that survived the winter move north and lay their eggs in Texas and southern United States. Each generation continues to move north. Nebraska’s monarchs are likely the second generation each year.

Unfortunately the monarch butterfly has declined 90% in the last 20 years. There are many factors contributing to the decline. Across the breeding grounds, grassland habitat that once had milkweed and blooming flowers throughout the season has been reduced. The use of herbicides, and the widespread use of neonicotinoid insecticides are also linked to the decline in monarch numbers. Another major factor contributing to the population decline occurs in the monarch overwintering sites in Mexico where to illegal logging in protected areas is eliminating the remaining monarch winter habitat.

The monarch butterfly is currently under consideration for protection under the Endangered Species Act. The International Union for Conservation of Nature (IUCN) has designated the monarch migration a threatened phenomenon. The Mexican government created the Monarch Butterfly Biosphere Reserve which protects 62 square miles of forests in the Sierra Madres, where hundreds of millions of monarchs spend each winter.

While there are many factors contributing to the monarch population decline, you can make a difference where you live or work. Learn more about gardening and habitat restoration for monarchs