Living With Forest Tent Caterpillars
Forest Tent Caterpillars appear in massive outbreaks every 8-12 years and the infestations can run for two or three seasons.
What are forest tent caterpillars?
Forest tent caterpillars are a native species in Canada and the United States. The name is a bit misleading because the caterpillars don’t spin the ugly webbed tents produced by other caterpillars, such as the eastern tent caterpillar.
The forest tent caterpillar is identified by a row of white key-hole shaped dots along the back and blue lines along the sides.
The caterpillars are often discovered in large in bunches on trees or found marching in long lines.
Check out our forest tent caterpillar vs eastern tent caterpillar page to see a comparison of the two caterpillars.
Ways to control Forest Tent Caterpillars
Homeowners can use high-pressure water spray to remove the caterpillars from individual trees.
To prevent the caterpillars from reaching the upper foliage of the trees, property owners can wrap tape or paper around the trunk and add a sticky substance called “Tanglefoot”.
Forest tent caterpillar moths lay eggs in tightly arranged bands on the twigs or branches of small trees. Homeowners can use clippers to remove the eggs and burn them. The easiest time to do this is in the fall after the leaves have fallen.
In situations where commercial forests are at risk of extensive tree mortality due to successive defoliation the woodlot owner can contract private companies to spray the forest.
The Ontario MNR and the Minnesota DNR both recommend spraying with Btk (Bacillus thuringiensis var. kurstaki), a biological insecticide which affects caterpillars of moths and butterflies that are out actively feeding at the time the spray is applied.
The insecticide is most effective when the larvae are small. This would normally be in May or early June. As the larvae get larger they can defoliate the tree before the pesticide has any effect.
The spraying should only be done in areas where people are unlikely to be in contact with the insecticide.
Natural control of Forest Tent Caterpillars
Nature also has its ways of controlling the caterpillars. In fact, rodents, bears, birds, and other insects take advantage of the bountiful larvae.
A forest tent caterpillar outbreak is usually accompanied by an increase in the population of a parasitic fly called sarcophaga aldrichi.
Also known as the “friendly fly”, this pesky bug is one of nature’s key tools for controlling the forest tent caterpillar population.
The Minnesota DNR says a massive increase in friendly flies often signals the end of a forest tent caterpillar outbreak.
The friendly flies deposit their maggots on the forest tent caterpillar cocoons. The maggots then dig into the cocoons and feed on the pupae, preventing them from reaching the moth stage of the life cycle.
Friendly flies look like a small housefly and can be more of a headache than the forest tent caterpillars. The flies arrive in irritating swarms and seem to enjoy landing on arms, legs, and any other human body part that looks appealing.
Another forest tent caterpillar killer
Maggots are rather disgusting but nature has another weapon for controlling the forest tent caterpillar that also causes some people to squirm.
Check out the amazing photos and incredible story about the Cottage Tips editor’s encounter with stinkbugs as they wiped out forest tent caterpillars on his cottage property.