Tiger swallowtails home-grown
Even among a group as collectively colorful as butterflies, the tiger swallowtail stands out.
The combination of bold black stripes on butter yellow, with a cluster of blue and orange spots along the bottom edge of the wings, makes tiger swallowtails easy to notice as they glide by or probe flowers for nectar.
The tiger also is among the largest butterflies in the Upper Peninsula, with only monarchs and black swallowtails comparable in size. And at the height of its seasonal flight, the tiger swallowtail occurs in numbers those other two species can’t match.
While the monarchs migrate back to the area — though a reader properly pointed out they don’t actually make the flight all the way back from the wintering ground in Mexico, but have at least one generation along the way before returning — tiger swallowtails are home-grown, hatched from pupae that withstood the long winter buried under leaf litter and a blanket of snow.
They emerge en masse once it gets reliably warm enough to sustain them, usually in late May and early June this far north, said Mark Scriber, a retired Michigan State University professor in Aloha, Michigan.
They commonly can be seen congregating around mud puddles — behavior he referred to as “puddling” — to draw up sodium and other minerals. Almost all of these are males, Scriber said, as the females will find their own spots to avoid being harassed.
Though they appear very similar, tiger swallowtails actually have two distinct varieties in both Wisconsin and Michigan, to the north and south, Scriber said.
Virtually all of what we see here in the Upper Peninsula is Papilio canadensis, the Canadian tiger swallowtail. Previously classified with the Eastern tiger swallowtail, Papilio glaucus, it earned full species status in the 1990s.
It’s a little smaller than the Eastern form and has some slight pattern differences on the underside of the forewing, Scriber said. It also will produce only one new generation a year and disappear by August, while the more southernly Easterns has enough time in a longer summer to crank out two rounds.
Though this might look like a fragile creature, the Canadian tiger swallowtail is impressively cold adapted. Like spring peeper frogs, this version of tiger swallowtail produces a form of natural antifreeze that allows its pupae to withstand even severe winters.
The result is tiger swallowtails can be found fluttering around Fairbanks, Alaska, and sub-arctic Canada, Scriber said.
Each tiger swallowtail species, Canadian and Eastern, have specific plants their larvae can feed on: the more northern type favors aspen, poplar and balsam, along with cherry varieties and ash; to the south, the tiger swallowtails primarily like the tulip tree and magnolias as well as cherry and ash. In fact, Scriber said, the two species have become distinct enough that tulip tree leaves are toxic for Canadian caterpillars, while the Eastern swallowtails won’t thrive on a diet of poplars or birch.
Where it gets interesting is in the middle zone, where the two varieties of tiger swallowtails mingle — and mate. Hybrids of Canadian and Eastern butterflies can be found in a belt across the middle of Wisconsin and Michigan east through New York, Pennsylvania and Massachusetts.
Hybrids can turn up where other closely related animal species overlap as well — it’s been well documented in birds, such as where the Baltimore and the more western Bullock’s orioles come together in Nebraska.
But something different happened with these hybrid tiger swallowtails. First, they were able to consume the host plant species of both parent varieties without ill effect, Scriber said. Second, they emerge in July, pretty much after the flights of the Canadians and between generations of Easterns.
So these hybrids usually had no other tiger swallowtails to breed with except other hybrids, Scriber said. The result has been the rise of a new species: Papilio appalachiensis, the Appalachian tiger swallowtail, named because it first was identified in the Appalachian Mountains, he said.
While the struggles of some butterflies, such as the monarch and Karner blue, have been alarming, tiger swallowtails for now seem to be holding their own. The fact they can use such a wide variety of host plants means they don’t take such a hit if problems develop with that host, as happened with the monarchs and milkweed.
They perhaps “are the most generalized feeders among swallowtails in the world,” Scriber said, adding, “I don’t worry about these populations at all.”
In fact, climate change might be leading the Eastern and Appalachian forms to expand northward, he said.
Sticking with cold-adapted butterflies, one native to the region hibernates not as a pupa but in full adult form: the mourning cloak, a velvet-brown variety that has golden edges on its wings along with a string of powder blue dots.
When cold weather sets in, the mourning cloak will tuck itself under leaf litter or into cracks and crevasses in rocks or trees that are sheltered enough to hibernate through the winter.
It can make for a startling sight in late winter or early spring, to have a butterfly flutter by on an early warm day in March, even as the last snow and lake ice might remain, said P.J. Liesch, entomologist for the University of Wisconsin-Extension in Madison.
It also makes these among the longest-lived butterflies in Wisconsin, up to 10 months, experts said.
Most butterfly and moth species spend much more time as larvae or pupae than as adults, Liesch said. Those earlier stages concentrate energies on feeding and developing; once an adult, the focus will be on mating and reproduction, with the mature insect usually not surviving much longer than a matter of weeks, he said.
The giant silk moths now showing up in the region, such as the polyphemus and luna, have only vestigial mouths and will not eat as an adult, Liesch said. Moths this massive are a tempting target anyway for predators, so it likely would have a short life even if it could feed, he noted.
Betsy Bloom can be reached at 906-774-2772, ext. 40, or email@example.com.