09/21/2017 04:19 EDT | Updated 09/22/2017 17:08 EDT

Southern Quebec visited by 'unprecedented' number of painted lady butterflies

MONTREAL — The millions of black-and-orange butterflies that have carpeted flower beds across the Montreal area in recent days are waiting for winds to carry them south to warmer weather, according to an expert at the Montreal Insectarium.

Southern Quebec has become host to an "unprecedented" number of painted lady butterflies in the last ten days, said Max Larrivee, the museum's head of research and collections.

"It's extremely unusual," he said in a phone interview Wednesday. "This is the largest on record — no doubt."

He said it's unclear precisely why the region has witnessed so many butterflies at once.

One factor that can explain the increase, Larrivee said, is that the butterflies arrived early this year and therefore benefited from an extra reproduction cycle.

Their large numbers, he continued, allowed the insects to cover a bigger territory than they normally would.

"In the spring they came really early and in really high numbers in April, which allowed them to take advantage of a much larger territory to reproduce, but also to reproduce one more time than they normally do," Larrivee said.

And while they usually fly up to 500 metres in the air, he said they've been forced closer to the ground by winds coming from the south.

Most of the painted ladies will probably leave Quebec to continue their southwest migration towards Texas and Mexico within a week or so, or whenever the winds shift, Larrivee said.

People often confuse the painted ladies with the monarch butterfly, which has similar colouring but is larger and has no brown on its wings or body.

And unlike monarchs, which feed only on milkweed, painted ladies can eat a variety of plants, which gives them a more expansive breeding ground.

Christian Schmidt, a research scientist with Agriculture and Agri-Food Canada, said large numbers of painted lady butterflies have also been spotted in other provinces including Alberta, B.C. and Nova Scotia.

"It's pretty much right across the country, although maybe not with the numbers you're seeing in southern Quebec," he said in a phone interview.

He too, said the exact reason for the population boom remains a mystery.

Possible factors include climate shifts and rainy spring weather leading to lush vegetation growth, he said.

"It's tough to say exactly what conditions are favourable to the population buildup," Schmidt said. "It's probably a combination of things."

While the painted lady butterflies have had "a phenomenal year," Larrivee said the same isn't true of most other local species, which suffered during a cold, wet spring.

"Overall some butterflies are faring well, some are faring poorly," he said. "The general consensus overall is that there are less butterflies than there used to be pretty much everywhere on the landscape."

Larrivee said he and other scientists are hoping to solve the mystery of the butterflies' shifting migration habits with the help of the public.

He's asking people to log into the website to document their pictures and observations of the insects.