Western Hemlock Looper (Lambdina fiscellaria lugubrosa)

The western hemlock looper (Lambdina fiscellaria lugubrosa) is a moth species native to our coastal forests. This moth contributes to the natural ecosystem cycles we have come to know on the North Shore. As the name suggests, this moth species, more specifically the larval stage, prefers to feed on the Western Hemlock tree (Tsuga heterophylla). However, during an outbreak, which occurs every 11 – 15 years and lasts 3-4 years, they can also be found feeding on western red cedar (Thuja plicata), Douglas-fir (Pseudotsuga menziesii), and even understory shrubs like red huckleberry (Vaccinium parvifolium). Notoriously known as ‘wasteful feeders’, the larvae eat small portions of many needles, which can cause tree death more frequently than other moth species that eat fewer whole needles.

Hemlock looper larvae can be 3 – 33 mm in length, and yellow-brown-grey in colour. They have a black head with pairs of dots along their body segments. Larvae emerge in the spring to begin feeding on new hemlock needles. As they grow over the summer months, their appetite becomes more voracious up until they metamorphose in September and October to mate. Adults have a 35 mm wingspan and mottled tan-grey wings with two distinct black lines across the wings outlined in yellow.

Populations are kept in check with cold snaps in the spring that kill some of the over-wintering eggs, or very wet fall weather that hinders moth flight and mating. However, a few years of warm, dry shoulder season weather can increase populations to outbreak levels. Currently, we are nearing the end of an outbreak on the North Shore that began in 2019.

Years of drought, in additional other pest and disease issues have caused coastal hemlock trees to decline. This current looper outbreak has been the last nail in the coffin for many hemlocks, and this is evident on our mountainsides by brown patches of defoliated and dead conifers. Fortunately, these dead pockets of forests allow sunlight to reach through the canopy and reinvigorate understory vegetation and increase biodiversity. However, if these outbreaks increase in frequency, the conifer covered mountainsides that have become the backdrop to North Shore living may start to change.