While we’d been busy banding birds, the Sun had climbed high into open skies above the Moquah Barrens on the spine of the Bayfield Peninsula. The temperature had climbed since early morning, too. As the group of students in the Wisconsin Master Naturalist Volunteer Training Course climbed back into our cars and caravanned through this U.S. Forest Service Special Management Area, yellow clouds rose up from the middle of sand roads.
Pulling into the Bladder Lake Recreation Area a few miles away, we were met by more yellow. Kathrine, one of the Museum’s new Summer Naturalist Interns, walked down to the sandy shoreline only to be engulfed in a swirl of yellow wings. I don’t think I’ve ever seen more Canadian tiger swallow butterflies in a single day!
This abundance of beauty has been building. On June 5, as I paddled the Namekagon River for a “Birding by Ear” field trip, occasional tiger swallowtails flitted along the shoreline. By June 10, we encountered half a dozen on the blackberry flowers at the trailhead for Morgan Falls—a hike that’s always a highlight of the Master Naturalist Course. And now it was June 11, and we were surrounded by their delicate yellow wings with black tiger stripes and scalloped edges leading into two little “swallowtails” at the rear.
As lackadaisical as the flight of butterflies may look, these butterflies are in a hurry to complete their life cycle in a brief northern summer. Visiting flowers to sip sugary nectar powers their flight. Males need some additional nutrients, too, and those come from something much less sweet than a flower.
Our vehicles disturbed clusters of butterflies on the sand roads. Their rising inevitably revealed a pile of animal scat. Male butterflies engage in an activity called puddling, where they lap up nutrients from the surface of puddles, or piles of poo. At Bladder Lake, they were puddling on a collection of decaying plants that had washed into a corner of the beach. The salts, proteins, and minerals they gain from this behavior get wrapped up in a nuptial packet and transferred to the female during mating.
Most if not all male butterflies engage in puddling, but it seems especially important for Canadian tiger swallowtails. Females must have enough energy to give their offspring a head start by laying large eggs; the nuptial packets are part of this. They also place their eggs, one per leaf, on the south side of trees. This provides more warming Sun exposure and less competition for the developing larvae.
As the temperature increases from 54 to 86 degrees Fahrenheit (due to normal changes in weather, or just a great location) the larvae can increase their growth rate by up to 500%. There is a catch, though. Larvae on birch trees won’t grow faster, even if it’s warm. Only the more nutritious leaves of aspen trees allow for such rapid growth. The butterflies must choose their host plants carefully, and hope that aspens are available, especially at the far north end of their range in Alaska and Canada. Apples and cherries are also possible host plants.
In a surprising but smart move, if a caterpillar survives a summer cold spell, they will then begin to grow faster. The longer and the colder it was, the faster the caterpillar will grow when it’s over—as long as they aren’t dead. Larvae with food in their guts freeze at warmer temperatures.
With all the poop puddling their Papas do, perhaps it’s fitting that young tiger swallowtail caterpillars avoid predation by looking just like brown and white bird droppings as they feed on the sunny surfaces of leaves. The older caterpillars costume themselves to look like mini snakes with leaf-green bodies and big yellow eyespots. They arm themselves with orange glands that emit stinky chemicals if disturbed. Despite those defenses, birds such as the gray catbird, rose-breasted grosbeak, and eastern towhee who we’d banded earlier that morning, probably eat many of them. As we’ve discussed before, one Being’s baby is often another’s baby food.
If they survive childhood, the larvae store up cryoprotectants to help them avoid freezing and then transform into pupae. Once properly hardened off and hidden away, the chrysalis can survive at least seven consecutive days at -2 degrees. The faster that a caterpillar can get to the safety of a cold-hardened chrysalis, the better—even if that means not growing as large. Smaller larvae result in smaller adults, but that didn’t seem to matter to the clouds of yellow and black butterflies rising in the sunshine.
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 is in the works—and needs illustrators from the community! Find out more at: https://www.cablemuseum.org/books/
For more than 50 years, the Cable Natural History Museum has served to connect you to the Northwoods. Our Summer 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.
Last Update: Jun 25, 2025 2:14 pm CDT
