MIKE MILLER

September is a month of culmination. The busy summer winds down towards a readying for winter. The quick pace of the summer katydid song on a warm August night slows as September’s nighttime temperature drops. The sounds of summer are winding down as many insects ready themselves for their ultimate demise by the hands of old man winter.

Not all insects settle for such a fate. Some escape the death grip through extraordinary means. Such is the destiny for the Monarch Butterfly. Their migratory feat is incredible and full of mystery and shows the miraculous ability of nature to adapt and the diversity of survival strategies.

Migration is not unfamiliar in the insect world. Many species of butterflies expand their territories north from the tropics where they can have year-round populations. Each generation moving further north as they reproduce. Monarchs, and several other species do this. What makes the Monarch butterfly unique is its strategy of taking four generations to move to its northernly limits in Canada, then creating a “super generation” built for travel that makes a journey 3,000 miles back south. That super generation overwinters in Mexico then travels back north around 300 miles to Texas in March.

Think about this for a minute …

How does that fourth generation know where to go? Their parents were never in Mexico, nor where their grandparents, or great-grandparents. Would any of us know the travel paths of our great-great-grandparents? It would take a lot of genealogical research for us to accomplish this feat. Somehow the Monarch does it instinctively. Not bad for a bug.

Migrating Monarch butterfly nectaring on New England Aster in September at Tawny Oaks Field Station in Peoria County.
MIKE MILLER

The “super generation” is thought to be created by Monarchs because of environmental factors such as the aging of milkweed plants and nectar sources. The seasonal reduction in the length of daylight is also a trigger. The “super generation” is built for travel; lightweight, strong wings, and an urge to fly south. They boast a refined neural system tuned for travel. Their antennae contain light-sensitive magneto-sensors that use ultraviolet and blue light to better orient them. Their antenna also contains neurons that serve as a circadian clock, allowing their brain to know direction by understanding the complexities of the Sun’s movement across the sky throughout the day. Combined with physical, environmental cues such as topography, wind direction and atmospheric pressure, they have a pretty good handle on where they are on the planet.

When it all works, it is amazing! Like many migrations, favorable weather conditions can build up waves of migrants. If you are in the right place, at the right time, you might be witness to thousands of Monarch butterflies traveling in a mid-September sky. As evening comes, they will seek shelter in trees near a nectar source. Hedgerows adjacent to fields with blooming goldenrod and asters are usable night roosts for Monarchs in our Midwest landscape. A prairie next to a forest is even better. Once they nestle in among the twigs of the trees, it is as if they are bringing their own version of fall color. An allusion of what is to come.

In the morning, as the sun evaporates the September chill, the Monarchs will flutter from the trees to a nearby nectar source to refuel for the day’s travels. As the Sun warms the morning, an urgency to move triggers them to take flight. A normal rate of travel will take them 30 miles south each day. If conditions are prime, they can cover 100 miles. It’s an arduous journey of 3,000 miles that might take a couple of months to complete. Eventually they will reach the Oyamel Fir Forests in Mexico and overwinter. In March they will move back north to Texas to start a new generation to carry on the multi-generational migration back to Canada.

Each year, a multinational group of scientists and volunteers monitors and protects the wintering grounds. Last winter (2025), most overwintering monarchs were gathered within a 4.42-acre section of the Mexican forest. This is twice the size of the 2024 overwintering population, so it shows that there is hope for the future. However, this hope is tempered by the reality that historic populations in the early 1990’s once covered almost 45 acres of forest.

We can learn a lesson from the Monarch. Their ability to survive is built upon a superior sense of place. They are inherently in tune with where they are upon the planet. One lesson from the Monarch is that our curiosity about how they survive has brought out the best in our species. Humans have grasped onto the Monarch as something worth saving. People across national borders, speaking different languages, and following different cultural customs all stand together in their desire for the survival of this charismatic insect. In their survival, we experience the best in ourselves. And that is a lesson worth having.