by Karen Oberhauser, Wisconsin Monarch Collaborative
A month ago, the southernmost roost sites reported by Journey North volunteers were in Oklahoma. As of this writing (October 29), the leading edge of the migration has moved well into Mexico (figure 1), with one sighting of 16 monarchs in the State of Guanajuato, the state just north of Michoacan where many overwintering sites are found. However, the main part of the leading edge is near Saltillo in the State of Coahuila. Based on these locations, the very first monarchs should begin arriving at their winter homes within a few days, right on time (they usually begin arriving around the Mexican Day of the Dead holiday), while larger numbers will be a week or so behind.
Note that the migration is very spread out at this point, with roosts and monarchs occurring much farther north than the leading edge. This is not uncommon; non-migratory monarch adults live and reproduce for about a month. Monarchs that emerge after about August 15 in Wisconsin will, for the most part, emerge in reproductive diapause (putting off reproduction until next spring) and migrate to Mexico. However, those that emerge before mid-August will lay eggs over the course of their month-long lifespan. So reproductive females (some that were born here and some from farther north) were laying eggs in Wisconsin until about mid-September. Because these late eggs are exposed to cool conditions, they take longer to develop, and emerge as adults well into October. In some years few of these late monarchs survive, but some will make it to Mexico, forming roosts and being spotted by Journey North observers along the way.
Figure 1. Journey North map downloaded 29 October 2025. For up-to-date details, click here
Late Season Monarchs in Wisconsin
As noted above, the migration is spread out in October. Wisconsin’s position in the northern part of the breeding range provides a front row seat to this unfolding spectacle! Butterfly observers reporting their sightings to Wisconsin Butterflies have continued to report monarchs, with the latest sighting as October 29 in Harrington Beach State Park (on Lake Michigan just north of Milwaukee), and late sightings in Grant County (October 23) and Olbrich Gardens in Madison (October 20). But these aren’t record late sightings for Wisconsin. Jay Watson, Insect Ecologist with the WI DNR, reported a monarch on November 14 in 2016, and a monarch was spotted in Dane County on November 13 in 2011. I spotted what is probably my last monarch of this year on October 17 in my yard, filling up on Mexican sunflower nectar (figure 2).
For more detail on how monarchs did in Wisconsin this year, see last month’s update.
Thanks to Journey North and Wisconsinbutterflies.org volunteers for providing the above data, and to Monarch Larva Monitoring Project volunteers for providing weekly reports throughout the summer.
If you’d like to help monarchs, one of the best things you can do is provide habitat for them. Check out the Wisconsin Monarch Collaborative website for great advice on how to do this. The Monarch Joint Venture has a free webinar series with exciting speakers every month, on topics ranging from fascinating biology to practical conservation tips.
