The North Shore is seeing a Western Hemlock Looper population boom that with probably last another year or two. Last year the moths were particularly abundant, though I’ve definitely noticed quite a high number this year as well. It’s a native species and is part of the natural coastal forest ecosystem that feeds on trees in the North Shore forested areas.
Outbreaks can last three to four years and we are currently in year two. While outbreaks are not uncommon and populations build every 11 – 15 years in the region, the moth populations could diminish next year or we may see another year of defoliation next summer. It all depends on weather and other environmental factors.
The moths primarily munch on Western Hemlock trees, but also feed on other hosts including Douglas-fir, subalpine fir, grand fir, and spruce when populations are high. Deciduous trees such as native maples and forest understory vegetation may also be hosts. Some trees that are less tolerant of being defoliated, western hemlock in particular, may succumb to the damage and, according to the District of North Vancouver’s info page, there is evidence already of mortality occurring in the hardest hit areas.
“Usually they collapse before they cause extensive mortality. They are short-lived and so not spraying is a wise move because the problem will go away”
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