The monarchs that migrate from the north to Mexico are typically the great-great-grandkids of the ones that made the same migration the year before. Non-migratory butterflies generally live less than a month as adult butterflies. Migratory monarchs live up to 7 months.

Most of the butterflies in the migrating generation are born in the northern United States or southern Canada in late summer. Instead of reproducing immediately after they emerge, these monarchs drink nectar to prepare for their journey south.

In late summer and fall, monarchs from Minnesota migrate more than 2,000 miles to the Oyamel fir forests west of Mexico City, where they winter. In the spring, they start back north, laying eggs in northern Mexico and the southern United States, where the migratory monarchs finally die. Their offspring continue the journey north to their summer breeding range.

The next few generations of their offspring concentrate on reproducing rather than traveling farther north. What Oberhauser calls "a significant portion" of the next migratory population comes from the Midwest.

While Oberhauser doesn't think the monarch will become extinct in Minnesota, she said the population could remain low permanently if habitat loss continues. This could jeopardize the migration because a smaller population is more vulnerable to storms or drought.

Andrew Wagaman