A rare kaleidoscope of painted-lady butterflies will invade Alberta this summer, during an epic migration that only happens every 10 to 15 years.

It's been a dozen years since the province was last inundated with the dainty insects.

"We get used to migrating birds coming north and south every year like clockwork, but some butterflies are not like that at all," said John Acorn, a naturalist known as the Nature Nut.

"And the painted lady is a great example."

The colourful butterflies breed in the southern United States, parts of Mexico and Central America.

Their migration into Canada is dependent on weather conditions and the health of those southern populations, said Acorn, a professor with the department of renewable resources at the University of Alberta.

'We expect to see our fill'

"As the population grows, the butterfly population becomes more migratory and they just stream north," Acorn said. "The bigger the population, the stronger the migration.

"We generally see a couple every year, but this year we expect to see our fill."

The painted lady is easily identified by pointed, salmon-pink wings, with intricate dark markings and row of five eyespots on the outer edges of the hind wing.

"The painted lady is more pinkish-orange but the butterflies that are arriving now are a little bit faded," Acorn said. "They've flown who knows how many hundreds, if not thousands of kilometres, so they're not looking their best.

"The butterflies that emerge in July will be much snappier looking."

Taking flight

It's not known exactly how many of the insects are expected to fly into Alberta this summer. But there will be ample opportunities to catch a glimpse of them before they fly south again or perish in the cold, said Acorn.

The butterflies arriving now will be laying their eggs on thistle flowers in a few weeks.

"I don't know how long they're going live, maybe a month or two if they're lucky," Acorn said of the butterflies soon to emerge from cocoons.

"There is some suggestion that they migrate south again at high altitudes before winter so it may be that they get out of here before it gets really ugly, although I have seen painted ladies into October and they didn't seem to get that this is Alberta and they should get out."