Photo Caption: A question mark butterfly, identified by the light, punctuation-esque marking on the underside of its hindwing, soaks up some afternoon sun.
Good Natured: Overwintering Butterflies
April 9, 2021
Butterflies are easy.
It’s a statement that naturalists make from time to time, and it refers to the fact that we don’t have to work very hard at all to get people interested in butterflies. Snakes and spiders, on the other hand, are tough, and slime molds are darn near impossible. But butterflies are easy.
Butterflies-some of them, anyway-also are early. And by this I mean that we have a handful of species that start flying in early spring, long before the species that have to progress through the caterpillar and pupation stages appear.
But wait, how can this be? We know our monarchs head to Mexico, but what about the others?
While some butterflies undertake much shorter migrations, and a few overwinter in the egg stage, most spend the cold weather months as caterpillars or pupae-both stages that will require additional development before the adult appears and starts flying around.
So what’s the story with the butterflies we’ve been seeing this past week? These beauties belong to a special group indeed: the butterflies that overwinter as adults.
In our area we have three species likely to be seen at this time of year: the mourning cloak, Nymphalis antiopa; and two types of anglewings, the question mark, Polygonia interrogationis, and the question mark, P. comma. (I’ll reserve the cabbage white butterfly discussion for another time. I’ve seen a few specimens of this introduced species flying already too. They overwinter as pupae, so the warm weather we had in March likely helped them “finish” quickly and enter their adult stage early in the season.)
As their name implies, mourning cloaks are dark brown, almost black, with a line of iridescent spots and a border of bright yellow. Anglewings, named for the irregular outer wing border, are primarily orange with dark markings on top, with grayish, bark-mimicking marks underneath. The comma is slightly smaller and is named for the light-colored “comma” on the underside of its hindwing. The slightly larger question mark has, go figure, a question mark in that same spot.
You might think that these special insects would need to find a way to stay warm all winter. We do, don’t we? Ah, but we don’t have the chemical makeup of a hibernating butterfly. As temperatures begin to cool in fall, mourning cloaks and anglewings produce large amounts of sorbitol and other chemicals that serve as natural antifreeze. Tucked underneath bark or under layers of undisturbed leaf litter, the butterflies survive quite nicely.
Then, as the days lengthen and temperatures begin to warm, mourning cloaks and anglewings emerge from their winter shelters and begin their search for first, food, and soon, a mate.
Of these two necessities, food can sometimes be the tougher one to find. Oak tree sap is the mourning cloak’s preferred food, but rotting fruit will do in a pinch. Anglewings seek out mineral-rich mud puddles, carrion and animal droppings.
As for that other priority, finding a mate, males adopt a sit-and-wait approach. They’ll camp out in a sunny clearing and wait for a female to come fluttering by. Eggs are laid on a variety of host food plants. For mourning cloaks, those include willows, elms, cottonwood, aspen, paper birch and hackberry. Host plants for anglewings include elms, willows and nettles.
Caterpillars of the three species differ in many ways-mourning cloaks, for example, live communally, while anglewings disperse-but both share the characteristic of bearing fierce looking spines down their backs. But while the mourning cloak’s can cause a stinging sensation, the anglewings’ purportedly are harmless.
Another big difference between the two species is that anglewings sport two distinctly different looks, depending on when they emerge. The winter form, which we’re seeing now, has orange hindwings, but the summer form, which flies during the warm-weather months, has dark purple hindwings. Mourning cloaks
As you consider how these butterflies spend their winters, you might be tempted to put up a butterfly house-those tall, decorative boxes with wide slits staggered along the front. Hey, if you like the way they look, go ahead! But don’t be surprised at who, or what, moves in.
Research has since shown that butterfly houses do indeed make great homes…but not for butterflies. In one study, 40 boxes were examined and found to be home to spiders, wasps, flies, ants and, in one instance, a white-footed mouse. Where were the butterflies? In their natural hibernation spots-under loose tree bark, leaf litter and brush piles. (All the more reason to get behind the current movement of Leave the Leaves, while also stacking brush in a quiet corner of the yard instead of hauling it to the curb for pickup.)
The researchers concluded that butterfly houses function well as garden ornaments but do little to aid the survival of our native butterfly species. A better tactic for those wishing to help butterflies, said one scientist, would be to build a mud puddle.
Now that’s easy!
Pam Otto is the outreach ambassador for the St. Charles Park District. She can be reached at 630-513-4346 or firstname.lastname@example.org.