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Red Admiral butterflies are often spotted in early spring. They may overwinter nearby as adults, or they may migrate back from their winter home in southern Texas. Photo by Ernie (Own work) [Public domain], via Wikimedia Commons.

Sunshine warmed our backs and a cool breeze filtered through bike helmets as we turned onto the pavement for a ride around the lake. Before we could get up a head of steam, Drew called back, “Did you see that butterfly?” In a flash my bike was on the shoulder, my phone was out with the camera turned on, and I was running back to where he pointed. 

I crept forward, struggling to discern the mottled brown underwings of a butterfly from the leaf litter. I must have gotten too close, because suddenly, in a flash of orange, white, and black, the butterfly rose and flitted erratically around a tree. My eyes darted along its wild flight path, and focused hard on the spot where it landed. Even knowing where I should look didn’t help. The butterfly’s wings melted into the gravel and leaves pushed aside by the snowplow. 

When I crept forward again, the butterfly startled and flapped its colorful wings deeper into the forest. I walked back to my bike. The elation of seeing my first butterfly of the year, combined with sunshine and a tailwind, inspired fast pedaling and a joyful ride. But a mystery gnawed at me, too. As far back as I can remember, Mourning Cloak butterflies have been the first to dance along on my early spring outings. Their deep-purple wings with yellow edging have brightened my day many times.

Mourning Cloaks overwinter in the Northwoods as adults, I’d learned, and I was astounded that such a delicate thing could survive our harshest season. Just like wood frogs and spring peepers, they have the advantage of waking up right near their breeding habitat, ready to go. 
Paging through my Kaufman Guide to Butterflies of North America, though, I’d decided I must have seen a Red Admiral butterfly. What does it do in the winter? I realized that besides the Mourning Cloak and the charismatic, migratory, Monarch butterfly, I had no specific knowledge about how butterflies spend the winter.

Happily, my Google search quickly turned up a wonderful document from UW-Extension listing the winter survival strategies of common Wisconsin butterflies. As with most things in nature, there’s no single answer. Butterflies can overwinter as eggs, newly-hatched caterpillars, mid-stage caterpillars (this seems most common), mature caterpillars, pupae, hibernating adults, or migrating adults. 

I also found a page on wisconsinbutterflies.org where butterfly enthusiasts post their most recent sightings. So far this spring, people have spotted Mourning Cloaks, Eastern Commas, Gray Commas, Compton Tortoiseshells, and Red Admirals. 
The first four species on that list all overwinter here as adults. As the autumn days shorten, antifreeze chemicals start building up in their body fluids. This happens for all the species who overwinter in the north, regardless of whether they chill as an egg, larva, pupa, or adult. Glycerol prevents ice crystals from growing and rupturing cells, even at temperatures well below freezing. So the adults tuck in behind loose bark, into crevices, or beneath logs, to sit out my favorite season. 

In spring, these adults obviously have a jump on everyone else. They don’t need to hatch, or grow, or metamorphose. They are ready to go. By basking in the sun and shivering their flight muscles, butterflies can raise their body temperature up to the 80 degrees F needed for flight, even while I’m still wearing my warmest cycling gloves. 

Red Admirals, like the one I saw, may have a different tactic…or maybe not. At least in the southern parts of their range (which extends from Guatemala to Canada), adults and pupae hibernate. How far north they can survive the winter seems to be up for debate, and the line could be shifting. The parts of their range where Red Admirals don’t survive the winter must be recolonized each spring by migrants from the south. The UW-Extension document asserts that our Red Admirals fly back and forth from south Texas.

Over the summer, Red Admirals have two generations. The summer brood is large and showy, with brighter colors, and a coming-of-age in July. Those butterflies produce a smaller, drabber, winter form, which we can see from late August through the first frosts. Just like with Monarchs, the winter form, although flighted, is not reproductively mature. They have a metabolism that allows them to pack away fat stores for migration and/or hibernation. 

They’d better have some fat left in reserve when they arrive up north in April! I’ve seen flowers blooming, but only if you expand your image of a flower to include catkins, the miniscule petals on hazelnut bushes, and a few other tiny tree flowers. Early butterflies do not arrive to a beautiful buffet. As anyone with a sugarbush knows, though, sweet liquid is plentiful if you know where to look. Conveniently, Mourning Cloaks may actually prefer tree sap to nectar. 

With early the snowmelt, I’ve been road biking a lot. It’s been easy to go fast while the forests are still quiet and gray. If this butterfly (and the loons, cranes, ducks, and frogs) are any indication, though, my rides are about to encounter many more distractions!

Special Note: Emily’s book, Natural Connections: Exploring Northwoods Nature through Science and Your Senses is here! Order your copy at http://cablemuseum.org/natural-connections-book/.  Listen to the podcast at www.cablemusum.org!

For 50 years, the Cable Natural History Museum has served to connect you to the Northwoods. Come visit us in Cable, WI! Our new exhibit: “Better Together--Celebrating a Natural Community” will open on May 2!