The amazing tale of butterfly 'ps 397' — which helped illuminate monarch migration

On this day 44 years ago, in 1975, I met two of my students, Jim Street and Dean Boen, from Hopkins North Junior High School on a Saturday morning to tag monarch butterflies at the University of Minnesota Landscape Arboretum's restored prairie in Chaska.

The morning began with a clear sky and a temperature of 47 degrees. Monarchs have difficulty flying below 55 degrees — and can't fly at all below 50. By 9 a.m. the air over the arboretum jumped up a bit above 55 degrees, and the 200 or so monarchs on the 10-acre prairie began visiting the flowers of blazing stars, goldenrods and sunflowers.

The three of us netted, tagged and recorded close to 100 monarchs in a couple of hours. With light pressure, we applied adhesive tags to the right front wings of the butterflies.

We got the tags from an associate of mine, Fred Urquhart, a renowned entomologist from the University of Toronto who had been investigating the monarch and its possible long-distance migration for more than 25 years. Each tag had a special number, along with "Send to Zoology, University of Toronto" in tiny letters. One monarch that we tagged Sept. 6 in the arboretum, numbered "ps 397" was picked up in January by Urquhart himself.

Condensed from Urquhart's letter sent to me immediately after the discovery:

"I found it on January 18, 1976, in the overwintering colony in the volcanic mountains of Mexico (a straight line distance of about 1,750 miles) at an altitude of approximately 8,500 feet, temperature about 34 degrees F.

"The way I found it was quite remarkable. A branch of a pine tree had been so loaded down with the weight of the butterflies that it had broken and thousands of butterflies were in an inactive condition on the ground. The photographer from National Geographic had asked me to sit down on the ground so that I would be surrounded by the butterflies. As I was sitting there, I reached into a pile of butterflies and was amazed when I picked up the tagged specimen, which, of course, the photographer snapped immediately. The butterfly was in excellent condition. I have had a lot of exciting experiences during the many years of this work, but I can safely say that this was the most exciting one I have ever experienced, thanks to the hard work of you and your students. This was the only tagged specimen that was recaptured in our three weeks stay in Mexico."

Ours was the first tagged monarch found in Mexico and was the proof needed to declare where monarch butterflies from eastern North America winter-over. We were written up in National Geographic (August 1976), and an IMAX film telling the story of migrating monarch butterflies was released in 2012.

Monarch migration is at its peak now, but we can watch them flying south overhead, one by one, into October.

Jim Gilbert's observations have been part of the Minnesota Weatherguide Environment Calendars since 1977. He taught and worked as a naturalist for 50 years.