How the Monarch Population Handles the Winter

Some butterfly species can overwinter as larvae, pupae, or adults; however, the monarch butterfly cannot survive the cold winters of northern climates. As the temperature begins to change, monarchs sense when it is time to begin traveling south to a warmer climate. During the annual migration to Mexico and California, the monarchs use air currents and thermals to travel long distances. It can take up to two months and 3,000 miles to reach their winter home.

When migrating, monarchs travel by day and roost at night. Roost sites provide an opportunity for the monarchs to gather close together during the cool nights. Pine, fir, and cedar trees are often chosen for roosting. Monarchs bask in the morning sun to warm themselves before taking flight again.

In North America, the eastern population of monarchs overwinter in Mexicos from October to late March. They roost in oyamel fir trees in the same mountain areas every year. The forest provides an ideal climate for the butterflies with temperatures ranging from 0 to 15 degrees Celsius. If the temperature drops, the monarchs cluster together to stay warm. Since the monarchs rely on their overwintering habitat, the Mexican government created the Monarch Butterfly Biosphere Reserve to protect them.

Monarchs that live west of the Rocky Mountain Range in North America overwinter in California. The conditions along the Pacific Coast near Santa Cruz and San Diego provide conditions that are similar to that of Mexico. Here they roost in eucalyptus, Monterey pines, and Monterey cypresses.

The monarchs lay the eggs of the new generation before it's time to make the journey back north. Once the days get longer and the temperature rises, the migration north begins. It will take three to four generations to reach the northern United States and Canada. Since all the monarchs are concentrated in just a few locations when they overwinter, harsh weather conditions and human activities can destroy their habitat. This and other factors have led to the decline of their species.

By planting and protecting local milkweed stands, the monarch's summer breeding grounds, people can help them get to Mexico and California and reverse the declining trends that have been seen the past few years. Monarch Flyway is focused on protecting pollinator habitat through market based conservation. Creating products with the renewable, natural resources of milkweed pods encourages wild, biodiverse areas and creates "Working Habitat" beneficial to people and the environment.