Looper moth outbreak in pacific northwest expected to continue for another year

SFU professor notes the outbreak can have positive side effects

PHOTO: Melissa McMasters / Flickr

Written by: Karissa Ketter, News Writer

Over the past few weeks, moths have been swarming Metro Vancouver. Native to North America, these insects are known as western hemlock loopers and phantom loopers, according to Dr. Gerhard Gries, professor of evolutionary biology and ecology at SFU. 

It has only been in recent months that those in the pacific northwest have noticed the moths crowding their homes, but as Dr. Gries states, “Outbreaks [can] last for two or three years,” and occur every 10–12 years. According to the District of North Vancouver, “we are currently in year two” of the outbreak. 

The outbreak of moths is not a new issue to North America. According to Natural Resources Canada, between 1910 and 1975 hemlock looper moths have “caused timber losses estimated at 12 million cubic meters in Newfoundland and 24 million cubic meters in Quebec.”

In an interview with The Peak, Dr. Gries noted that the surplus of moths “may be caused by a combination of two factors: really warm summers that stress the trees and [ . . . ] a mild winter that allow[s] eggs to survive.” He added that “there is no definitive answer” to why their species has seen a jump in population but ecologists can continue to “speculate on this.”

Dr. Gries stated that the moths have the potential to affect our ecosystems in numerous ways. The huge populations of larvae are “[defoliating] the trees” — which means that as they feed, they strip the trees of their leaves. Dr. Gries said that when “the defoliation is severe, then the trees may die.” He added that local parks and green spaces will notice defoliated and weakened trees due to larvae damage. However, the District of North Vancouver noted that “it will require years of decay before trees become structurally weaker.” 

Dr. Gries discussed some positive effects of forest defoliation on the forest floors. As the moths are feeding on the foliage of the trees, they are opening up with the forest canopy, allowing more light to reach the forest floor — this “encourages regeneration to happen.” This is spurred on by the larvae’s preference for feeding on older trees, leaving space for new trees and foliage to grow in their place. 

This process is aided by the larvae’s feces, which becomes a natural fertilizer that further encourages the growth of new foliage. 

The government of British Columbia has outlined the ongoing short-term and long-term strategies to anticipate and “predict levels of defoliation.” This includes conducting egg sampling in the fall that an outbreak is predicted to anticipate the amount of defoliation that will occur that summer. 

“There are no practical measures we can take” to control the moth populations at this time, according to the District of North Vancouver. While the moths can be overwhelming in some areas, they are asking that those affected have patience. 

If a large tree on your property has died and become hazardous, there is a service that can be used to report it. For more information on reporting tree issues, visit their website

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