Butterflies on the Move
Every fall, North American butterflies head south without a map. The most famous are monarchs. The ones east of the Rockies leave Canada and the northern U.S. in late August and September and aim for a few fir forests in central Mexico. Some travel 3,000 miles. The wild part is that no single monarch makes the round trip. The butterflies arriving in Mexico are the great grandchildren of the ones that left last spring.
West of the Rockies, monarchs fly to the California coast instead. They crowd into eucalyptus and pine groves and hang from branches like orange leaves until the sun warms them.
Other butterflies migrate too. Painted ladies move north in spring as plants green up, then drift south again in late summer. Cloudless sulphurs and gulf fritillaries head for Florida, the Gulf Coast, and Mexico. Red admirals travel in looser groups. You just notice more of them one week and fewer the next.
They migrate because winter kills their food. Frost wipes out nectar flowers and the plants caterpillars eat. As days get shorter, a hormonal switch tells fall monarchs to stop breeding, store fat, and fly. Those migrators can live eight months. Summer monarchs live only a few weeks.
The trip is risky. Storms, cars, pesticides, and lost habitat all take a toll. You can help by planting native milkweed and late blooming flowers like goldenrod and asters. Skip fall yard cleanup so they have nectar. If you spot a tagged monarch, report it.
It is quiet compared to bird migration. One day your garden is full, the next day it is empty, and a tree in Mexico gets a little heavier.