Leonard Weber

September 11, 2023

There are many Common Milkweed plants in Eliza Howell Park, in various locations, and I sought out a significant number of them on my most recent walks in the park.

By the second week in September, the seedpods have developed but are not yet open for dispersal of seeds. Many of the leaves are yellowing.

September is the month when most of the Monarch butterflies that we see in Michigan leave on their migration to Mexico, flying something like 50 – 100 miles a day, for a total of about 2000 miles.

I suspect that many of us, if undertaking a journey like that, would want to be ready ahead of time and get an early start. But it is not unusual to find Monarchs still in the caterpillar stage, eating milkweed leaves, in the second week of September. They have not even begun the final stage of metamorphosis.

On September 10 and 11 this year, I saw several caterpillars, each appearing to be nearly full size.

When I see Monarch caterpillars this late in the season, I wonder whether they might be late for migration. Many Monarchs are already migrating through this area, but most typically leave Michigan on their migration to Mexico in middle or late September, according to published reports. These Eliza Howell individuals will have to spend appropriately 10 – 14 days in the chrysalis stage before they can even fly for the very first time.

These new adults that migrate south in the fall have a much longer lifespan than their summertime parents, who only lived a few weeks. These, if all goes well, will make it to Mexico, spend the winter there, and start back before they stop in the southern U.S. in early spring to breed (and then die).

Just as they somehow know the way to the wintering grounds without having been there previously, some of the next generation will find their way here next May, never having been here before. And some of the same milkweeds, being perennials, will be here to host them.

There is still time, but if they succeed in emerging from the chrysalis as adults, they will not have much time to drink nectar and try their new wings before undertaking that enormous migration feat.

I have known about Monarch migration for a very long time, but as I watch these caterpillars eating milkweed leaves in September, I find myself again totally fascinated by nature’s wondrous ways.