If you recently felt a wee yelp of pure joy coming through the celestial strings that connect us all, that was me, reacting to the pleasure of seeing my first butterfly of the year.
It was April 11, a lovely, sunny day, and I was out in Taylor Creek Park to see how spring was progressing in my local branch of the Don watershed. As I strolled along the trail, I caught a glimpse of something dark fluttering about on the trail in front of me.
A brief look was enough for me to be almost certain I’d seen a mourning cloak, (Nymphalis antiopa), one of Toronto’s many resident butterflies.
Mourning cloaks are one of the easiest of all butterflies to identify. From a distance, these large, distinctive insects look nearly black. But peer closely and you can see their special beauty: their deep maroon wings are trimmed around the edges with a ragged ribbon of the palest yellow, and inside the yellow edge are a row of tiny spots of vivid electric blue.
Most of the butterflies that biologists consider to be breeding residents — meaning that they are present all year in the Toronto area — overwinter in their immature forms. That is, they survive through the cold months as eggs, caterpillars or chrysalides. But mourning cloaks are among the nine species of butterfly in Ontario that hibernate through the winter as adults.
In the fall, as the cold weather begins to set in, mourning cloaks locate a nice crevice in some rocks or a tree, crawl under some loose tree bark, or tuck themselves into a sheltered spot in a building to wait out the worst of winter.
But how do they manage not to freeze, especially after the kind of winter we’ve just endured?
Noted butterfly expert Peter W. Hall, a retired research associate with the Canadian National Collection of Insects, Arachnids and Nematodes in Ottawa, was kind enough to answer my questions.
Hall says most insects that live in cold climates like ours have salts in their bodies that lower the freezing temperature of their body fluids. Many insects, including the mourning cloak, can also produce glycerol, which acts as antifreeze enabling them to withstand winter temperatures as cold as -40 C.
Mourning cloaks stay safely tucked out of the wind in this state of torpor during the frigid months. If there’s a sunny day in late winter that warms up to at least 10 C, these butterflies may emerge and fly around, if only briefly.
As Hall explains, mourning cloaks are able to generate enough heat to activate their muscles by first “shivering” in their protected hideout.
Once they’ve activated their muscles, they climb out of their crevice to find a warm spot in the sun, where they sit with their wings open. “This helps the dark wings to better absorb the heat from the sunlight,” he says. The radiant energy from the sun further powers their flight muscles to enable flying.
But what happens to these delicate creatures if the temperature should plummet again? That’s what happened in Toronto after I saw mourning cloaks flying on the weekend of April 11. On April 13, the high recorded at the airport was 22.7 C; on April 16, the overnight low was -6.9 C.
I wondered if the butterflies I had seen would be killed by the frost. Or, with their muscles slowed down once again by the freezing temperatures, if they would become easy meal targets for all our returned songbirds. I needn’t have worried.
“If the temperatures drop again,” Hall explains, “then the butterfly will search out the same or another hibernation site and settle back into it. They can then hibernate again until the temperatures warm once more.
“Just last week, I watched a mourning cloak later on an afternoon as the temperature dropped,” he continued. “It settled at the base of a tree with a hole in it and then climbed steadily back up into the hollow of the tree.”
You have to hand it to that clever Mother Nature for combining the magic of insect antifreeze with the instinct for survival.
Keep your eyes open the next few weeks before the trees leaf out completely and you might see one of these dark beauties. Look for them sheltering in white oaks, basking on fallen logs or in the leaf litter, or perching nearly motionless on the trunks of trees like black willow or hawthorn, where they feed on the tree’s sap.