Making Unique Observations in a Very Cluttered World

Thursday, 19 April 2012

‘Tidal wave of butterflies’ hits Toronto - the biggest springtime butterfly migration in history -

‘Tidal wave of butterflies’ hits Toronto - the biggest springtime butterfly migration in history - 

Butterflies may not grow on trees, but it’s starting to look like they do.

Eastern Canada is in the midst of what’s believed to be the biggest springtime butterfly migration in history. Hundreds of thousands of butterflies have made their way north — many more than usual and much earlier than expected.

While butterfly observers are in a frenzy, others are wondering where they all came from. And with Thursday’s forecasted high of 22 C in Toronto, the new arrivals will be out and about and hard to miss.

“There’s never been anything like this. This is like a tidal wave of butterflies making their way north,” said Jeremy Kerr, a biologist at the University of Ottawa.

Glenn Richardson, president of the Toronto Entomologists’ Association who’s been observing butterflies since the late 1960s, called it “the largest migration that I’ve ever seen.” He estimates the population is 20 times higher than usual.

About 90 per cent of the butterflies are red admirals, easily identified by their dark brown, red and black wing patterns. They are common in Ontario summers, but spend winters in the southeastern U.S.

Abnormally warm weather down south — the U.S. had its hottest March ever — created ideal conditions for the insects to grow and populate. That heat also cued the northern migration.

“Normally what would happen is … they’d hit some really cold zone and they would lose the ability to disperse in that area — they would stop,” said Kerr, who leads the Canadian Facility for Ecoinformatics Research. “But they were hitting temperatures they would expect to find at the end of June, so they just kept going.”

And with strong southern winds earlier this week, the record number of butterflies invaded much sooner than usual. By Tuesday morning they were spread across Ontario, New Brunswick and Nova Scotia. Maxim Larrivée, a postdoctoral fellow working with Kerr, said they have travelled 300 to 400 kilometres per day.

Although it’s difficult to pin down exact numbers, Kerr said there could be millions of butterflies across Eastern Canada. Larrivée said one man found an estimated 20,000 butterflies in the backyard of his London, Ont. home and there are other reports of butterfly-covered trees.


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