Monarch butterflies, one of North America's most common butterflies, has a very unique migration pattern. The Monarch butterfly migration begins when cold sets in during the autumn months in the northern United States and southern portion of Canada. To escape the coming cold winter, the monarch butterflies move south and west. They generally begin the migration in October, however that can differ depending on the weather.
Monarch butterflies travel from east of the Rocky Mountains tend to migrate to Mexico, while the population west of the Rockies generally migrate to Southern California. Even though the butterflies arriving are the fourth generation since the ones that were there the previous year, they still hibernate in the same trees as last year's monarch butterflies. Monarch butterflies larval food plants do not grow in the areas where they spend the cold weather months, which is why they have to then migrate back to northern areas in the spring so that they can complete their life cycle.
There are four generations of monarch butterflies each year, and they go through four stages in the butterfly life cycle. The first state of the life cycle is the egg. Then comes the larvae, which is a catterpillar. Then the pupa forms, also called a chrysalis, and lastly the adult monarch butterfly emerges. Each year that process happens four times with four different butterflies. Once winter is over, the last generation of the year emerges from hibernation and finds a mate. They travel north or north and east and lay their eggs on milkweed.
This begins the new first generation of the year. Once the eggs hatch, it takes about two weeks for the caterpillars to reach maturity. Then they find a stem or leaf to attach to and form the chrysalis. After ten days, the monarch butterfly emerges. The butterfly lives between two and six weeks and will die after laying eggs for the next generation. The second generation is born in late spring and the third is born in mid-summer.
The first three generations of butterflies each year go through the same life cycles and life spans, however the fourth generation is a little different. This generation is the one that will migrate south, and because of this they will live 6-8 months until the process begins once again.