Butterfly Survives Illinois Winters

by Dee Hudson Photography

As the temperatures drop below freezing, I find myself wondering where this Mourning Cloak butterfly will stay during Illinois’s cold winter. Perhaps it will find a cozy tree hole, a warm hollow log or nestle in a space behind some tree bark. This butterfly better find a good shelter, because rather than migrating to someplace warmer, this butterfly stays here in Illinois for the whole winter. Brrrr! How is survival possible? Well, this butterfly has a high level of sugar in its cells that act like antifreeze, allowing the Mourning Cloak to survive without freezing. Very cool (or should I say ‘very warm’)!


It was June 21,st and I was pulling unwanted sweet clovers from a restored prairie planting at Nachusa Grasslands. As I neared some common milkweed in bloom, I first spotted this large brownish butterfly feeding on the pink flowers. Sometimes they feed on the flower nectar, but normally they drink tree sap — especially oak sap. I had my camera with me, the light was soft and pretty and the Mourning Cloak cooperated for a few shots before flying away.

I was amazed with the perfect condition of the butterfly’s wings. I’m guessing the Mourning Cloak was probably newly emerged from its chrysalis, because in Illinois, the adults tend to emerge in June and July. The temperatures on the prairie in the summer months can be pretty hot, so the Mourning Cloak has a unique way to survive. The butterfly finds a coolish resting place, then lowers its metabolic rate and takes a nice summer nap until the temperatures are more reasonable. By spending dormant time in both the summer and the winter, this butterfly actually lives over ten months — a long life for a butterfly!

Hike through the prairie in late March or April and watch for the Mourning Cloaks, for they will probably be the first butterfly you see emerge in the spring. Surprisingly the butterfly may even be seen flying over the snow on a warm day. Let me know if you spot any!