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Fewer monarchs arriving in northern Ontario, researcher says

Jul 29, 2022 11:16AM ● By Content Editor
Photo: Monarch butterflies travel migrate north up to 4,000 kilometres each year. (Mary Garshore/Nature Conservancy of Canada)

By CBC News Staff - CBC News - July 26, 2022


The migratory monarch butterfly is on the red list of threatened species — two steps from extinction — after the International Union for Conservation of Nature officially declared them endangered earlier this month.

Northern Ontario scientist Cass Krane, in fact, says fewer of the subspecies are making it to the region. 

Monarchs, known for their spectacular annual journey of up to 4,000 kilometres, travel from Mexico and southern U.S states like California, ending up as far as northern Ontario. 

"They require one specific group of plants, milkweed, in order to live," said Krane, who's on staff at Science North. "Caterpillars only eat this one plant. It's essential to them. 

"So things like herbicide use and habitat loss can have a really significant impact on their population."

In 2016, the monarch butterfly was designated as endangered by the Committee on the Status of Endangered Wildlife in Canada. Now, to help track the declining populations, researchers are enlisting the help of citizen scientists.

"There are apps like Journey North and iNaturalist where people can take pictures of the butterflies," Krane said. "They can upload those pictures … iNaturalist will even help you identify it …. and then where you took that picture is now tagged in this database."

Monarch caterpillars like these are often found on the underside of leaves from the milkweed plant. (April Douglas (@seaglassheart)/Twitter)

Scientists then collate the data to see where people are taking photos of the monarch.

"That is actually a big part of the reason how we know that the monarch butterfly population is declining," she said.

Once their numbers decline, there's no predicting what effects that could have in the ecosystem, Krane said. 

"We never know what's going to happen in the environment if we lose the species until, unfortunately, we lose that species," Krane said. "Also, the fact that what's threatening these monarch butterflies are threatening many insects." 

Several other insects, like the American burying beetle and the coral pink sand dunes tiger beetle, are also on the endangered list. 

"If you think of a food chain, most food chains have as their base an insect," Krane said. "So to lose insects is to lose this key link in the food chain. And that could have a disastrous impact on the world."

Monarch caterpillars feed exclusively on the leaves of milkweed. (Amy Hadley/CBC)

Butterflies could be adapting to climate change

But in Mexico, experts said, 35 per cent more monarch butterflies arrived this year to spend the winter in mountaintop forests, compared to the previous season.

That may reflect the butterflies' ability to adapt to more extreme bouts of heat or drought by varying the date when they leave Mexico.

The government commission for natural protected areas said the butterflies' population covered 2.84 hectares this year, compared to 2.1 hectares last year.

The annual butterfly count doesn't calculate the individual number of butterflies, but rather the number of acres they cover when they clump together on tree boughs.

Gloria Tavera, regional director of Mexico's Commission for National Protected Areas, said logging in the butterflies' wintering ground rose by about 4.5 per cent this year, to 13.9 hectares.

However, fewer trees were lost to fire, drought, or plant diseases and pests. So overall tree loss in the 2021-22 season was 18.8 hectares, down from 20.2 hectares in the 2020-21 season.

"They are beginning to adapt to extreme climate conditions," Tavera said.

Strangely, this year, the butterflies stuck around in Mexico longer than usual. "They left very late. We still had butterflies in April," Tavera said.

It remains to be seen in next year's figures whether that strategy worked for them.

While activists and students in the United States and Canada have been urged to plant milkweed, to make up for the losses of the plant due to the clearance of farm and pasture land and the use of herbicides, that strategy has backfired in Mexico.

Tavera urged Mexicans not to plant milkweed in Mexico, saying it might disrupt the migration by encouraging monarchs to stick around, rather than leave for the north.

She also urged people not to breed monarchs in captivity — they are sometimes released at weddings or other celebrations — saying that could spread diseases among the insects.



To read this original story and more news, follow this link to the CBC News website.

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