Revelstoke’s western hemlock looper moth outbreak natural: Parks Canada

The last large outbreak was in 2002/03

As with the butterfly, the flapping of the Western hemlock looper’s wings is not without wide-ranging implications.

An outbreak of the native moth species is reported from the Lower Mainland to the Interior, including Revelstoke.

Natalie Stafl, Parks Canada ecologist, said outbreaks of the moth occur roughly every 20 years in the Interior.

The last major outbreak for Revelstoke was in 2002-03 and a smaller one in 2012.

This spring, Stafl said Parks Canada staff reported large numbers of caterpillars falling from the trees, which indicted a start to the outbreak.

A Western hemlock moth caterpillar. (Lorraine Maclauchlan photo)

Stafl said an outbreak can last up to four years, with moth populations growing each year. This is year one.

Some nights, large clouds moths can be seen flutting around lampposts around Revelstoke.

“They look like a snow storm,” Stafl said.

Building in the downtown core, such as the Regent, are covered.

Eventually, the moth populations crash as predators, such as birds, also boom in numbers. Outside of outbreaks, the moths are present in very low numbers.

Since Interior rainforest is not usually susceptible to fires, said Stafl, insects are the biggest disturbers.

She said Parks Canada monitors insect outbreaks each year, from Douglas Fir beetle to spruce beetle and hemlock looper.

Since Revelstoke is in the early stages of the moth outbreak, the extent of damage will not be evident until 2022, said Stafl.

Outbreaks of the moth typically occur in hemlock stands, but occasionally they will erupt among stands of Douglas fir – something that has been seen this year across the province.

“The larvae – commonly called loopers or inch worms – feed from June through August and can strip trees of their foliage in a single season, sometimes killing large swaths of forest,” said Lorraine Maclauchlan, a B.C. forests ministry entomologist, in an email.

“The moths emerge in September and can be seen in trees, on the ground and resting on tree trunks until early October. The moths are mating and laying eggs during this time.”

“This outbreak is a concern because it may kill or weaken an already susceptible and highly pressured forest resource – both from a habitat and timber production standpoint.”

READ MORE: Several unique-to-Canada species found near Revelstoke

The province is currently surveying and assessing sites for consideration of targeted control programs next summer using the biological insecticide Btk (Bacillus thuringiensis), which targets the larvae.

Maclauchlan said Btk has been used by the ministry for past outbreaks in high priority areas, to protect critical habitat and key Crown land.

Outbreaks were likely not as extensive in the Shuswap in the past, said Maclauchlan.

However, along Highway 1, east of Revelstoke, Maclauchlan said evidence of past looper-caused mortality is visible, where large areas of forest were killed.

Stafl said the hemlock loopers will keep flying around Revelstoke probably until October, laying eggs and/or overwintering in bark crevasses until next year.

–With files by Lachlan Labere

Parks CanadaWildlife

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A Western hemlock moth caterpillar. (Lorraine Maclauchlan photo)

This year’s Western hemlock “looper” moth outbreak has been seen in the Lower Mainland and the Interior, including communities throughout the Columbia Shuswap Regional District. (Lorraine Maclauchlan photo)

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