Look closerInsects
Monarch migration through Sudbury: the generation that flies to Mexico
When: August to September
Monarchs emerging in eastern Massachusetts from about mid-August on put breeding on hold, live for months instead of weeks, and fly all the way to mountain forests in Mexico.
Why this time of year
The switch happens around mid-August: monarchs emerging in the eastern United States after that point are the migratory generation, so a monarch in a Sudbury meadow from mid-August on may be Mexico-bound.
How to notice it
- Check milkweed patches and stands of nectar-rich late-summer flowers along meadow edges and roadsides.
- Look under milkweed leaves for striped caterpillars; the ones growing up now become the travelers.
- When an adult monarch leaves a flower, notice whether it wanders between blooms or presses off in one steady direction.
- A grown-up can help you report a sighting to Journey North, which tracks the migration.
Try this with kids: Can you find a striped monarch caterpillar hiding under a milkweed leaf?
Scientists call this pause on breeding reproductive diapause; the energy saved goes into the flight south.
Sources
- journeynorth.orgMost monarchs emerging after about mid-August in the eastern US enter reproductive diapause; migratory adults live up to nine months versus two to six weeks for summer generations; they funnel to oyamel fir forests on Mexican mountain slopes.
- journeynorth.orgThe northward journey takes multiple generations, but on the way south the same monarch travels the entire way to the overwintering sites.
In the guide for August, September