The eastern Monarch population has one of the most amazing migration stories. It's just astounding. I honestly think I was slack-jawed the first time I heard it. Depending on where they begin the journey, some from as far north as Canada, they have to travel up to or more than 2,000 miles to reach their overwintering location among the Oyamel fir forests of central Mexico in the Monarch Butterfly Biosphere Preserve. There, crowded together, they hibernate for about four months, usually until March.
With the arrival of spring, they mate and fly north, eventually laying eggs on milkweed plants in the southern US. But this is just the beginning of a multigenerational flight north. Those lucky enough to survive to the butterfly stage then fly further north and lay eggs and this cycle is repeated three additional times. By the time Monarchs arrive here in the New York area, they're generally the third generation of butterflies, with those born in June and July usually making their way north yet again to as far north as Canada.
At each step of the northward journey, the Monarchs need milkweed plants for their caterpillars to consume because Monarch caterpillars are specialists and rely solely on the milkweed genus of plants (Asclepias) to develop. In the Eastern US, Common Milkweed and Rose Milkweed are often preferred milkweeds for egg-laying Monarch caterpillars, which are the two species we grow the most.
On the migration southward in the fall, their needs are for nectar-providing plants like those in the Aster family. New England Aster, Showy Goldenrod, Late Boneset and others that bloom in September and October are perfect for Monarchs to fuel up on for the four to six week journey where they average about fifty miles of flight distance per day. The fall migration is truly the ultramarathon of the insect world and they need wildflower nectar stations to sustain them to their destination.
And the great news is that we can help them with both legs of their migration by planting milkweeds, asters, bonesets, and goldenrods. Even better, all of these plants help other insect and bird species at the same time. In helping one, we can help many, and we can also broaden our planting in gardens and meadows to include a diverse group of native plants and create thriving ecosystems in the process.