Monarch butterflies are travelling south on a journey of as much as 3,000 miles, heading toward the forests where their ancestors spent the winter even though the individuals making the flight have never taken that route themselves. The autumn migration is now under way across North America, and some eastern monarchs cover up to 3,000 miles, or 4,800 kilometres, to reach the mountain forests of central Mexico, while most monarchs east of the Rocky Mountains aim for Mexico’s oyamel fir woods and many western monarchs pass the winter in sheltered groves along the California coast. The insects on this flight belong to a long-lived migratory super generation that can live for up to nine months and come through winter before starting north again in spring, whereas earlier generations typically survive only two to six weeks as adults, and the southbound travellers are several generations removed from the butterflies that last occupied those wintering grounds. The journey depends on both fuel and weather, since nectar supplies energy while favourable winds and rising air currents help them cover long distances without constant flapping, so that during the day they stop at flowers to feed and at night they may gather in sheltered trees, forming temporary roosts that hold hundreds or even thousands of butterflies. Peak migration generally moves through the central United States during September and farther south through October, and many eastern monarchs reach central Mexico from late October into November, although weather can shift the timing. To spot them, look for late-blooming flowers in parks, gardens and meadows on sunny days, and near sunset or early morning watch for clusters resting in trees, while leaving native autumn flowers standing and avoiding pesticides can help provide safer stopovers, native milkweed supporting the next generation by feeding caterpillars and nectar fuelling the migrating adults.