Butterfly Breezes of Fall

A gentle breeze rippled the surface of Gabimichigami Lake. Paddling steadily in the bright sunshine of early afternoon, we were grateful that it wasn’t a steady wind. More than a mile of open water surrounded us with no islands or points to hide behind as we crossed from one portage to the next on our annual Boundary Waters canoe trip.

Hillsides of young aspen and birch glowed golden in the distance. At first, a flutter at the edge of my vision made me think that an autumn leaf had somehow managed to fall half a mile to the middle of the lake. A closer look revealed the dark purple wings of a mourning cloak butterfly. In late September?

I’ve often looked for mourning cloaks in early spring, knowing that these are one of a few butterflies who overwinter as adults and emerge as the snow is melting. They feed mostly on tree sap, fruit juices, and the honeydew excreted by aphids, so it’s not hard for them to find food even before most flowers bloom. They make the most of sunshine even on cold days by spreading their dark wings and body to absorb warmth.

A mourning cloak butterfly suns themselves on a paper birch tree. Photo by Emily Stone.

The adults mate and lay eggs even before the leaves of their larval host plants emerge. After the caterpillars hatch and feast on willow, aspen, birch, or a variety of other tree leaves for a couple of weeks, they form a pupa. After another couple of weeks, they emerge as adults in June or July. This seems perfectly timed to take advantage of peak flower availability, but abundant nectar doesn’t tempt them to feast. Instead, the new adults pause their development and go into a period of dormancy similar to hibernation, called estivation.

Then, in September and October they begin another active period, presumably to build energy stores before their winter round of hibernation. While mourning cloaks aren’t considered migratory, there’s some evidence that some individuals do migrate, perhaps to find a slightly warmer place to overwinter. Wherever they go, they’ll snuggle into hollow logs, wood piles, and loose bark. Hopefully, wherever they hibernate also gets blanketed by insulating snow and becomes part of the stable environment of the subnivean zone.

Throughout the trip, I saw at least half a dozen mourning cloaks out over the water, dancing in and out of the dappled sunlight at our campsite, and briefly landing to bask on sunny, warm rocks. Seeing them reminded me of an early spring hike up to St. Peter’s Dome, when I photographed a mourning cloak sunning themselves on a birch tree.

Mourning cloak butterflies become active in fall after a period of summer dormancy. This one photobombed a sunny afternoon on Saganaga Lake in northern Minnesota.

Photo by Emily Stone.

It’s not a bad schedule, really. Emerge into the gently warming days of spring. Take a siesta during the hottest days of July and August. Enjoy a fall feast before tucking in for the winter. They use this plan to survive across North America and even in Asia and Japan.

I even spotted one mourning cloak as recently as last week on the Superior Hiking Trail above Silver Bay, Minnesota. After watching their irregular flight until they disappeared in to the forest, a flutter at the edge of my vision caught my attention just in time to watch an autumn leaf come to rest on the ground.

Small quaking aspen leaves carpeted the trail in a mosaic of yellow and green. They were evidence of yet another way that a Lepidopteran (butterflies and moths) survives the winter. Green leaves don’t usually fall from the tree, but the trapezoids of chlorophyll captured between the first and second veins on one side of the leaves’ midribs told me all I needed to know. These were the larval home of a tiny moth.

A moth larva creates this green and gold pattern in quaking aspen leaves.

Photo by Emily Stone.

Back in July, a small, brown moth with white-fringed wings laid an egg on the leaf petiole. By September, a translucent larva hatched and bored into the leaf’s petiole, causing the stem to swell into a small gall. Munching her way up inside the leaf under the cover of darkness, the leaf-mining larva interrupted the mechanisms the tree normally uses to draw chlorophyll out of the leaf during the waning days of autumn.

Such a tiny caterpillar would dry out in the summer heat if she tried to pupate high in the tree canopy. Instead, she timed her life cycle to hitchhike on a falling leaf down to the damp forest floor. Now there, she is stealing a few more bites of the green energy she’d hoarded in the leaf. Presently she will pupate in relative safety and an agreeable microclimate. The soon-to-be-moth spends the winter in her cocoon, which is loosely woven to the surface of the now-brown leaf.

Colorful leaves and colorful wings flutter on fall breezes, all getting ready for winter.

Emily’s award-winning second book, Natural Connections: Dreaming of an Elfin Skimmer, is available to purchase at www.cablemuseum.org/books and at your local independent bookstore, too. Natural Connections 3 will be published in November 2025!

For more than 50 years, the Cable Natural History Museum has served to connect you to the Northwoods. Our Fall Calendar is open for registration! Visit our new exhibit, “Becoming the Northwoods: Akiing (A Special Place). Follow us on Facebook, Instagram, YouTube, and cablemuseum.org to see what we are up to.