Western Hemlock Looper Moth Outbreak Continues

August 30, 2021   

We have been receiving many calls from concerned residents about the increase in brown trees and moths around the City. 

We are in year three of a Western Hemlock Looper Moth outbreak. Outbreaks typically last up to four years, and occur every 11 to 15 years. First came the larva-stage, and moths are now hatching and will soon be out in full force. Don’t be alarmed, these moths are a native species and this outbreak is part of the natural forest ecosystem cycle. 

During the larva-stage, the Western Hemlock Looper Moths feed on trees leading to defoliation of many trees in the City, including western hemlock, western red cedar, and Douglas-fir and Cypress. Although the defoliation can cause significant damage to trees and the brown trees look quite distressing, not all damaged trees will die. Many will regenerate given the proper conditions.

Tip: Want to keep the moths from gathering around your home? Moths are attracted to lights, so try turning off your exterior lights and close windows or use screens to keep them out of your home.

Western Hemlock Looper Moths


Brown Trees

Trees have been under additional stress this year due to extreme heat, drought and the Looper Moth outbreak.

There are no immediate measures we can take to control this outbreak, but City staff are monitoring the situation and have increased street tree watering to help reduce the stress on the trees. Although dead and dying trees are visually worrisome, overall fire risk is not greatly increased. Trees decay quickly adding to nutrient and sunlight availability and encouraging new understory growth within a short time.

Affected trees may appear dead without the green needles on the branches, but many of the trees are still alive and may eventually recover. Though the caterpillar damage is very stressful for the trees, the healthy ones will eventually leaf out again if given the proper conditions.

How can you help?

The best way to help stressed street trees and trees on your property is to ensure they have adequate water around the root zone area. Please give trees near your property a good soaking at the base of the tree trunk. This will allow the roots to absorb nutrients from the soil for use in the recovery process. 

Looper Moth tree damage at Mahon Park


What we’re doing?

The City is actively monitoring the health of the urban forest, and aligning our response with the other municipalities on the North Shore and working with Metro Vancouver and the Province of BC. Although there are no immediate measures the City can take to control the outbreak, we are working with our partners to assess the damage to our forests and determine potential next steps. 

Learn more at cnv.org/LooperMoth.

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