Migratory butterflies moving through Calgary during glorious two-week lifespan

Butterflies are always a sign that summer is in full swing. This year, there seem to be more than usual of the small, pale yellow butterflies flitting about Calgary.

Naturalist John Acorn says they're called clouded sulphur, and that they're in the process of moving through on their annual migration.

"There are about a dozen species of sulphers in Alberta, but two of them are migratory: the clouded sulphur and the orange sulphur. And so that's what we're seeing is a mix of those two species on the move through at least southern and central Alberta."

Two-week lifespan

Acorn, who lectures at the University of Alberta, says the winged beauties have just a two-week lifespan as a butterfly.

"They go through multiple generations through the summer, so these are probably the grandchildren of the first of the 2019 sulphurs," he said. "They generally move north in the early part of the season, in the spring and early summer. And they generally move south in the late part of the season. They've moved through generations."

Acorn says the butterflies move with the season and with the food supply, which for them is clover and alfalfa.

"It's kind of the same reason that that birds migrate. It's miserable here in the winter and there's lots to eat in the summer," he said.

"But a female clouded sulphur can lay as many as 600 eggs. So if every one of those little eggs survived, then all of a sudden you know you'd run out of clover and alfalfa. So it's not a bad strategy to expand the range early in the year and then contract again in the fall."

Acorn says the short lifespan also means they spend more time as a caterpillar than as a butterfly. 

"They don't have fancy hairs or patterns on them, they're generally greenish. Some of them have a nice little yellow stripe along the side and they're quite a classic caterpillar. Just a little green smooth critter."

The butterflies that live longest around here will hibernate over the winter — which sulphurs don't do, he says, adding that it's difficult to track the distance that a butterfly can travel.

Migratory butterflies

"We know there are other species of migratory butterflies — the monarch, of course. There was a record of an Alberta monarch captured in Mexico at the over-wintering site, so it probably went more than 3,000 kilometres," he said.

"And then we had another migratory butterfly coming in earlier in the year, the painted lady. And they may still make a big appearance this year. Painted ladies start their flights from the southern states and northern Mexico, and the farthest north I heard of painted lady, a worn out painted lady, this year was Yellowknife."

Acorn says his wife spotted a painted lady last month in Yellowknife.

"So they can really move when they want to. And especially if they get a good weather system pushing them as well."

So what are the odds of a Calgarian spotting a more exotic butterfly than these sulphurs?

"It depends on how much glory you've got on your lawn, I guess, but the adult sulphurs would certainly come to various types of flowers to get nectar."

So what does this flush of butterfly colonies say about the state of the environment?

"We try to monitor butterflies to see how things are going. But with a clouded butterfly like a clouded sulphur or an orange sulphur, what you would be monitoring is kind of the state of the entire North American environment," Acorn said.

"So if they failed to show up year after year after year, then we would worry. But, you know, amazingly enough there seems to be a nurturing environment to the south of us. So that's good. That's reassuring."

With files from the Calgary Eyeopener.