An Exciting Time of Year!
article by Karen Oberhauser
Figure 1. Photo and report submitted to Journey North by Opal in Rapid River MI. For full details, click here.
The second half of August is a particularly interesting time to observe monarchs in their northern breeding range. Beginning on about August 15, monarchs emerge from their pupae in diapause[1]. Responding to cues that include both daylength and sun angle, these adults do not become reproductive soon after emerging. Unlike their parents and grandparents, who were ready to mate and eggs at three to five days of age, these butterflies will delay reproduction until the following spring. Instead of putting all their energy into mating, producing eggs and sperm, and laying eggs, they’ll store fat and begin the long migration to their wintering sites in central Mexico for eastern North American monarchs and coastal California for western North American monarchs.
But there are still plenty of monarch adults around who emerged before August 15. These butterflies are mating and laying eggs – they may be moving south to give their offspring a better chance to survive upcoming fall weather conditions, but they won’t make it to the wintering sites. So at this time of year, you might see eggs and larvae on your garden milkweed, females laying eggs, males chasing females, and adults flying southward. If you’re lucky, you might even spot a monarch roost. You can keep track of what’s happening with monarchs by checking out Monarch Larva Monitoring Project graphs to see the density of monarch eggs and larvae in Wisconsin and Journey North fall roost reports. As of September 2, there has only been one report of roosts in Wisconsin (in Hortonville). Figure 1 shows an impressive aggregation in Peninsula Point, on Michigan’s Upper Peninsula.
[1] Diapause is a pause in development. It is a hormonally controlled state that allows insects to survive harsh but predictable environmental conditions. It can occur during the egg, larva, pupa, or adult stage, but in a single species the stage is consistent. Monarchs diapause as adults, but other butterfly species can diapause in other stages.
Monarch Larva Monitoring Project volunteers documented strong egg and larva densities throughout July and August (see figure 2 for Wisconsin data, patterns in other states are similar). The first eggs observed in Wisconsin were laid by the first generation of 2026 that came up from the southern US, so numbers of eggs and larvae observed in May and early June reflect how well this first generation did in the south. 2026 started out with few monarch observations (see low values in the first half of May) but picked up in late June and July.
For more detailed comparisons across years see Graphs of egg and larva densities per milkweed plant on the MLMP website.
Figure 2. Wisconsin MLMP data from 2026 (top left), 2025, 2024 and 2023. July and August 2026 densities are similar to 2025, higher than 2024, and lower than 2023, documenting year to year variation but no strong upward or downward trend. Note different scale in the different years, and the fact that 2026 isn’t complete.
Because monarchs need to eat as they migrate southward, migration success depends on nectar availability. Plants produce less nectar when conditions are dry. The current drought map for the U.S. (figure 3) shows a dry outlook as monarchs move southward. Wet conditions along rivers and low areas will be important sources of the nectar needed to fuel the migratory flight.
Figure 3. NOAA drought map. Downloaded from https://droughtmonitor.unl.edu/ on August 28, 2026. To compare other years, visit the Drought Monitor website.
Thanks to Journey North and Monarch Larva Monitoring Project volunteers for providing the above data, and the U.S. Drought Monitor team (the National Drought Mitigation Center at the University of Nebraska-Lincoln, the National Oceanic and Atmospheric Administration, and the USDA) who provide important statistics on drought conditions throughout North America.
If you’d like to help monarchs, one of the best things you can do is help provide habitat for them. There is a great Monarch Joint Venture webinar coming up on September 22—Seeds of Change: How Volunteers Power Prairie Restoration. See details here.
To learn more about what’s happening with Wisconsin monarchs, check out the August 26 Lee Rayburn show on WPR (also includes interviews about bird migration and mercury in our environment).
