August is monarch butterfly month in Minnesota, where this insect was chosen to be our official state butterfly in 2000. We see them between May and October, but we’re most aware of this wonder of an insect in later summer when their population is the greatest and when there are obvious aggregations of them roosting in trees.
Monarchs travel individually, not in flocks, but they do stop and gather together in roosting trees to spend the night, or days and nights if there is stormy weather. If there is a nearby field or natural prairie with good plants for nectar, they’ll gather there. They congregate in the late afternoon into the evening on the east sides of trees so the next morning’s sunlight can warm them up and get them going.
Monarchs continue their migration through the state during September and into October. At an average flight speed of 11 miles per hour, the first ones will reach their wintering sites in the mountain forests northwest of Mexico City close to Nov. 1.
Monarchs will fly anywhere from ground level up to 7,000 feet, the cruising altitude of many light airplanes. They save energy by riding thermals — rising air masses that lift them to favorable altitudes. Their soaring skills are so efficient that many arrive in Mexico fat and healthy, having gained weight on the trip. Yes, they do stop and drink nectar along the way.
I have been tagging monarchs since the 1970s. One individual monarch butterfly tagged by two junior high students and me, their teacher, from Hopkins schools Sept. 6, 1975, on the Minnesota Landscape Arboretum prairie, was recovered on Jan. 18, 1976. Fred Urquhart, a monarch researcher from the University of Toronto, captured it in an overwintering colony in the volcanic mountains of Mexico. The butterfly flew a straight-line distance of about 1,750 miles. Ours was the first monarch ever recovered and provided the proof that monarchs from northeastern North America winter in forested mountains of Michoacan, Mexico.
Jim Gilbert’s Nature Notes are heard on WCCO Radio at 7:15 a.m. Sundays. His observations have been part of the Minnesota Weatherguide Environment Calendars since 1977, and he is the author of five books on nature in Minnesota. He taught and worked as a naturalist for 50 years.