Hello fellow readers, It’s the unofficial start to summer which brings on outdoor activities and vacations including tent camping for diehards. Ben from Bangor asked what to do about the wormy things building tents in the crevices of his cherry tree right above his grill.
Eastern tent caterpillars, or tent worms (Malacosoma americanum), are the larvae of a species of moth known as lappet or snout moths. They’re more of an eyesore than a threat. I think of them as diehard campers with a nifty lifecycle. It’s true, though, when they fall on your plate at a barbeque, they’re rather icky.
Tent caterpillars prefer to camp in cherry and other hardwood trees. While they can significantly defoliate, they usually won’t kill trees. They say they can be toxic to horses, mules, and donkeys. If necessary, you can destroy the nests by dropping them into soapy water or opening them with a stick to expose the critters to the elements (away from livestock to be safe). Or there are environmentally friendly pesticides such as Neem Oil or Bt (Bacillus thuringiensis) you can use.
Eastern tent caterpillars appear in early spring and rely on the sun’s heat to elevate their body temperatures to allow them to digest food. The tents act as miniature greenhouses that are water-repellent, trapping the morning sun’s heat and offering protection from predators. Their tents also provide a respite for the social larvae which live in a commune with others. At their last larval stage, the caterpillars leave the shelter, and each constructs a cocoon in a separate protected spot and no longer live communally. The adult moths emerge about two weeks later.
The adult moth lays her single batch of 200 to 300 eggs in late spring. Within three weeks, fully formed caterpillars form within the eggs and lie inactive until the following spring when they chew their way out of the eggs, just as the leaves of the host tree develop. They feed thrice daily, before dawn, mid-afternoon, and sundown. During each bout of feeding, the caterpillars emerge and add silk to the tent. They move to distant feeding sites, eat, and then return to the shelter where they rest until it’s the next time to eat. Eat, Rest, Eat. Sounds like a perfect vacation!
You’ll enjoy a story titled Fall Webworms vs. Tent Caterpillars, also featured in Episode 71 of the Garden Dilemmas Podcast:
Side Notes: While small infestations can be taken care of by dropping the nests into soapy water, contact insecticides work best for larger populations. Bacillus thuringiensis (Bt) is the most effective and is a naturally occurring bacterium common in soils. It’s a selective insecticide that kills tent caterpillars while remaining safe to other wildlife. Apply the spray directly to foliage and tent worm nests.
It takes a few days, but why it works: Bt produces proteins that react with the cells of the gut lining of susceptible insects. These Bt proteins impact the digestive system causing the insect to stop feeding within hours. They then die from starvation, which can take several days.
Another option is Neem Oil: Read about it here Finding Neem Oil.
Column updated 8/28/22