ST. LOUIS, Mo. – You may have seen more butterflies in Missouri during August and September. They are making their annual epic trip back to Mexico from the northern United States. You can track their progress using this map made by citizen scientists.
Millions of Monarch Butterflies roost in the Sierra Madre mountain range in central Mexico during the winter. It starts getting warmer in the spring and this triggers their migration. By the middle of March, it is time for the insects to start flying in mass to the north.
The Monarchs fly north through Mexico to the southeastern corner of the United States, laying eggs as they go. They look for milkweed and other nectar sources to help feed the caterpillars.
The new generation picks up the next chapter of the migration. In June they fly into the northern United States and southern Canada.
Cities and agriculture have disrupted some of the Monarch’s migration. They need milkweed to survive and the plant is not as widespread before. Conservationists recommend planting milkweed and other sources of nectar to help the butterflies thrive.
In late August the butterflies start their journey back south to their wintering site in Mexico. They gather in thicker and thicker ribbons as they fly.
The Monarch travel during the day and roost at night. They may gather together during cool fall evenings. They gather in the same spots year after year.
By the time they hit Texas in late October the clouds of them stop people in their tracks. Hundreds of thousands of them flow like a river through the sky. Tens of millions of them arrive in their mountain roosts in November.
No one butterfly completes the whole journey. It takes up to four generations to finish the whole migration between the northern United States and Mexico.