Western Hemlock Looper Moth Outbreak

July 21, 2021   

Have you noticed 'inchworms' dangling from trees in your neighbourhood, lots of needles raining down or brownish trees? You might already be seeing moths, though they won't appear in full force until August.  

This is all related to an outbreak of Western Hemlock Looper moths, which is causing damage to trees and forested areas across the North Shore. The outbreak, which started in 2019, appears to be quite significant, but it is not abnormal and in fact is part of a natural ecosystem cycle. The best course of action is to let nature run its course, be diligent with monitoring efforts and alter activities as necessary..

Every 11 to 15 years, the moth population spikes and, while they're still in the larval phase, they feed on the needles of trees, causing them to turn orange or die. Outbreaks typically last about three to four years, and we're currently in year three. Trees that suffer a low or moderate amount of defoliation typically rebound, but ones that are already stressed or nearing the end of their natural lives will likely die.

There are no immediate measures we can take to control the outbreak, but Park staff are adding a second watering truck to increase watering and reduce the stress on the trees and are also coordinating their efforts with other North Shore municipalities. 

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.

Learn more at cnv.org/LooperMoth.

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