Not only birds but also butterflies fly long distances during their lifetime to faraway places. About 200 species are known to do this regularly, but other species sometimes start migrating, too. They all do this to escape cold seasons or because the population gets too big. This means not enough food and the danger of transmitting diseases to the next generation.

Light, wind and gravity are used for orientation. Migrating butterflies can even cross the sea: Columbus saw swarms of butterflies on his way to America.

The monarch butterfly from North America is a well-known example for the migration of butterflies. There are two migratory populations. The southern population flies to sunny California for the winter, the eastern-central population migrates thousands of miles south into the mountains of Central Mexico.

This is where we are now. In a small forest there is a swarm of about 40 million monarch butterflies. They have come a long way from Canada. When the sun comes out, they start flying around, sucking nectar and mating. It is March at the moment.

In April they reach the Rio Grande and cross the border to the USA. It’s time for the females to lay the first ones of their 400 eggs. One female tastes with its feet if the plant it sits on is good for a caterpillar to grow on. If this is the case, it lays one egg on the bottom of a leaf and goes on with other milkweed plants. It keeps on doing this while slowly moving farther north.

At the beginning of May it is somewhere in the southwest of Texas. Its wings show traces of the dangers it saw. Its journey will end here with its death.

But the next generation will continue the migration. After some days the first caterpillars hatch, but many of them won’t survive their first days. They are eaten by predators or die because they ate the wrong parts of the plants.

The ones who survived look for a place to pupate and do it. When they have hatched, they mate and start flying north. On their flight the females keep on laying eggs on milkweed plants. At the beginning of June they are somewhere around Washington DC.

Soon the next generation, the third one, will hatch and continue the journey farther north. The granddaughters of our first female will lay their eggs in Pennsylvania and, after having crossed the border to Canada, somewhere near Toronto.

The caterpillars hatching from these eggs will develop into butterflies that don’t eat for their eggs. These monarchs must store energy for their long journey back south.

It is getting autumn already. In swarms the butterflies start to fly southwest. With the help of the wind they cross Lake Erie. Warm up-currents carry them about 7,000 meters high. In a gliding flight they come down, covering long distances. In doing so they only have to move their wings 5 to 12 times a minute and only use one per cent of the energy needed for fluttering.

In October they reach Texas and in late autumn they arrive in the mountains of Central Mexico. They will rest here during the winter to mate and start flying south when the sun will "wake" them up in spring.

Originally, the monarchs only moved to the Plains in the Middle West in summer. But seemingly they had to change their destination because human agriculture didn’t leave enough room for their food plants.