Western Hemlock Looper

The western hemlock looper is a native defoliator of western hemlock, western redcedar, interior spruce and Douglas-fir.

This insect periodically reaches outbreak levels, causing severe damage to forests in both Interior and coastal stands in British Columbia.

The Southern Interior Area manages western hemlock looper damage by monitoring populations in susceptible stands. When significant damage is predicted, plans are developed to reduce defoliation through targeted aerial spraying using the biological insecticide Bacillus thruringiensis var. kurstaki (Btk).  


Although outbreaks are short-lived (one to three years), the wide range of host species and ages, and extensive feeding on foliage of any age, results in high levels of mortality in heavily defoliated conifers. Loss of valuable timber, increased fire danger risks, and loss of important wildlife habitat can result from hemlock looper outbreaks. 

Biology & History

Larvae hatch in the spring and feed lightly during May, June and early July, then voraciously from the middle of July to October.


Long-term strategies focus on stand management, while short-term strategies include monitoring and biological insecticides.