On a rare sunny day in Denali National Park, I was ambushed by surprising wildlife: butterflies fluttered and flashed everywhere — large yellow-and-black swallowtails, ghostly Arctic whites and black and orange alpines as dark as their own shadows.
I was surrounded. Like scraps of color, they littered the roadside rocks, touched down on the gravel road and tumbled everywhere. I was near Wonder Lake, at an elevation of roughly 2,000 feet, not exactly a tropical climate. As I watched the dazzling number of fluttering suspects, I wondered one simple question: How do butterflies, so ephemeral and delicate, survive in Alaska?
The butterflies weren’t talking, so after my trip, I spoke to Dr. Kenelm Philip, a senior research scientist at the Institute of Arctic Biology at the University of Alaska Fairbanks. He is working on carrying out a survey of Alaska butterflies, from the Arctic to Southeast Alaska. He says there are approximately 84 species statewide, with about 23 occurring in Southeast Alaska.
The limiting factor, Philip said, isn’t winter temperatures. Arctic butterflies can survive temperatures that drop to 40 degrees F and below. Summer is the tricky part. That’s when butterflies need to be warm enough to fly. Places with cool, rainy summers, such as Southeast, have fewer species than in the Interior, where summers tend to be hotter.
Depending on the species, butterflies may overwinter at any stage of life: as eggs, caterpillars, pupae (the stage when the insect changes from caterpillar to adult), or adults. In places with milder climates and longer summers, butterflies can produce more than one brood of eggs in one summer. This means some broods live out their life cycle in only a few weeks, although one brood will usually overwinter. Short Alaska summers mean only one brood for our butterflies, which must overwinter. This means Alaska butterflies can live more than a year.
It may seem like a superpower for a fragile adult butterfly to survive an Alaska winter, but it’s really more of a secret weapon. First, the butterfly finds a sheltered place to hide, a nook between tree roots, perhaps. A covering of snow adds more insulation. When the temperatures drop, the butterfly’s body produces glycerol, a chemical that drastically lowers the temperature at which ice crystals form. This prevents ice crystals from developing in the insect’s tissues and blood, which would damage cells. Combined with a sheltered, insulated hiding place, this natural antifreeze allows the butterfly to hibernate through the winter.
The Mourning cloak and Milbert’s tortoiseshell butterflies are species that hibernate as adults. These are often some of the first butterflies to appear in the spring. Sometimes they shake off their winter slumber before flowers start blooming. Philip said in this case, they may drink tree sap for sustenance.
Warmer spring temperatures heat the butterflies out of hibernation, stirring them back to life. Then, they face a new set of challenges. Insects don’t produce body heat like mammals, so they rely on outside heat sources — mainly sunlight.
Sunbathing is not just a vacation hobby for butterflies, it’s a necessity. Although the patterns on butterfly wings and bodies may seem like flights of fancy, they serve a practical purpose: dark colors absorb heat from the sun. Butterflies have different strategies for basking, depending on their coloration. Some species can increase their body temperature by nearly 20 degrees Fahrenheit above the surrounding air temperature.
Butterflies that live in the Arctic tend to be darker than their cousins of the same species further south. Females tend to be darker that males, since they need more energy to produce eggs.
Some species that have dark colors on the outside of their wings will stand with their wings closed, angling the surface of their wings to catch the most rays. If the butterfly becomes too warm, all it has to do is turn so its wings are edge-on to the sun.
Butterflies with dark colors on the insides of their wings bask with wings open. Still others have dark bodies but light-colored wings. By opening their wings at just the right angle, they reflect sunlight off the wing surfaces and onto their dark bodies. There is even a butterfly that frequents south-facing rock slides, pressing its wings to the sun-warmed rocks for a heat source.
Hiking up Perseverance Trail one sunny summer day, I spotted small, pale blue butterflies along the sides of the trail. They seemed to gather in platoons at the edges of puddles or even just damp places along the trail. Instead of basking in the sun, they were busy drinking or licking the mud. This behavior is called “puddling.” Butterflies can’t always find all the nutrients and minerals they need in sugary flower nectar. A damp place where minerals from the soil have leached into water is like butterfly Gatorade, providing a mineral and nutrient boost.
The blue butterflies on the trail were most likely Spring azures. Other common suspects you may find around Juneau include Margined whites, small white butterflies with gray bodies and faint gray lines on the veins of their wings, and Mourning cloaks, which are dark brown butterflies with a yellow band bordering their wings. Milbert’s tortoiseshells may also be lurking about, with their dark brown wings showing flashy orange and white stripes around the edges and small orange patches across the tops.
Painted lady butterflies occasionally fly up from the Lower 48, but Philip said a more likely scenario if you find these butterflies is that they are escapees from classrooms. Teachers will sometimes acquire the caterpillars so that kids can watch the insects go through their life cycle. Once they become butterflies, the kids usually release them.
Adult butterflies, if they feed at all, often drink nectar from flowers. They aren’t terribly picky though. These tough little survivors will feast on other natural liquids that offer nutrients if the opportunity arises, including urine, feces, carrion, or the sweet “honeydew” aphids produce. Flowers, however, are still the best place to lie in wait for them.
Good places to track down the colorful culprits in Southeast are open meadows with blooming wildflowers. Alpine areas seems to be good as well, especially on a sunny day, or at least out from under shady trees. Whatever the location, the sight of a butterfly dancing through the air like a paper-thin fragment of stained glass is one to treasure.
• Beth Peluso is a freelance writer and illustrator and an avid birder. She enjoys spying on wildlife across Alaska. Special thanks to Dr. Kenelm Philip and Bob Armstrong for information on Alaska butterflies.