Forest Tent Caterpillar

Many of you may have noticed, or have heard horror stories, of the current outbreak of Forest Tent Caterpillars in our area. Currently, the PeaceRiver region is experiencing a severe infestation and the population is steadily moving south. The City of Grande Prairie is asking all residents to routinely monitor any trees on their property for signs of these pests. There are small populations of the caterpillars already within city limits; however, if conditions remain favourable the city is very concerned about a severe infestation in our area next summer. When the caterpillar population is high they cause massive defoliation. This obviously makes the trees unsightly but even more concerning is that multiple years of this defoliation can severely weaken or even kill young trees.

So what exactly is the life cycle of the Forest Tent Caterpillar and how long will we have to endure the sight of the wriggling pests? Outbreaks usually occur every 6 to 16 years. Most outbreaks do not last more than 3 consecutive years. The larvae emerge from egg bands on the tree branches in the spring. By mid to late June they are approximately 45 to 55mm in length. The larvae construct their cocoons and the moths then emerge from mid-July to early August. After mating, the females deposit the egg bands containing 100-200 eggs on the branches of the host trees. And then the cycle continues!!


Cocoon image courtesy of


Adult image courtesy of

In order to help control the spread of the population homeowners can prune out the nests containing the eggs in the spring. Later in the life cycle, as where we are now, a pesticide is likely the only option to keep the population low. Check with your favorite garden centre for the most appropriate treatment for your trees/plants. There are natural factors that do help to keep the caterpillars in check. Disease, parasites and adverse weather are a few of these. Starvation is another natural factor but that only occurs after they have eaten every last shred of foliage on our trees!

Residents can do some pre-planning this winter/spring to help manage the outbreak. Neighbourhood Associations are a great way to help get the residents in the area on board and controlling the spread of the caterpillar.

Information on life cycle courtesy of Agriculture Canada

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Helen Harder

Helen Harder

CENTURY 21 Grande Prairie Realty Inc.
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