Fairy Ring Tree Care

Tree Pests

Forest Tent Caterpillar


This serious pest seems to have an outbreak approximately every 10 -15 years. They feed mainly on aspen and poplar, but will take advantage of any foliage they can get. Forest tent caterpillars are approximately 40-50 mm in length when fully grown. They are a dark brown colour with blue bands along their right and left sides. A row of white markings is present all along the centre of their backs.


The adult moths can be found mating from July through August. Once mating is completed, the females will lay their eggs in structures known as egg bands. This is where the forest tent caterpillar gets its name as the egg bands containing 100-200 eggs resemble small tents within the branches of the tree. The larvae emerge from their protective egg bands in the spring. This emergence usually coincides with the appearance of leaves on the host trees. The larvae will feed on the newly sprouted foliage till mid to late June. Depending on the number of caterpillars present, damage can range from a light thinning to the complete elimination of the foliage present. If the cycle continues heavily for 3-4 years the host tree may die. In most years the tree will usually re-foliate, either later the same year or the next.


Weather, loss of the food source, disease, predators and parasites all play a major role in controlling forest tent caterpillar populations. If possible you may be able to remove the egg bands from the affected trees in late fall or early spring. If you are using an insecticide to control this pest, ensure you follow all the directions on the label before and while applying. Ensure you apply early in the spring when damage is minimal and the larvae are small.

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