Gardening column: It’s a good year for tent caterpillars | Columnists

Eastern tent caterpillars are having a family reunion in the Lowcountry this year.

This insect usually goes unnoticed this time of the year, but every several years they come to party. You may have noticed them clumping together on tree trunks or one lost on the sidewalk. These hairy little things are 1 to 2 inches long with white splotches down their backs and cobalt blue spots down their sides.

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Tent caterpillars build webs in tree branches, where they are protected as they eat and grow. In general, they won’t kill a tree. Once they emerge from the webs, they can become a protein-rich meal for birds and mammals. Tony Bertauski/Provided

They hatch in late winter to early spring and feed on trees such as wild cherry and maple. They spin a silken web in the crotch of branches similar to fall webworms. Fall webworms, however, hatch later in the growing season and build webs at the end of branches. They are more common in the landscape than Eastern tent caterpillars.

Eastern tent caterpillars molt five times, growing larger with each molt. They hang out in the web for protection, expanding it as they grow. Caterpillars are juveniles in the lepidopteran order. Like most teenagers, they eat everything in sight. By now they’ve reached their maximum size. It’s time they become adults. That’s why we’re seeing them wandering around the Lowcountry.

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For insects, becoming an adult is easy. They simply leave the nest in search of a place to spin a cocoon. They’ll go through the stage of pupation, an idle stage where they’ll transform into a tan moth. The adults won’t damage trees. They’ll spend the rest of their lives looking for a mate to lay eggs for next year. The female can lay as many as 400 eggs. The larva that hatch the following year are social and will stay together to build another web.

Why are there so many Eastern tent caterpillars this year compared with previous ones? It could be due to weather or lack of predators. Plenty of things feed on them, from parasitic wasps to fungal disease. The predator/prey relationship often goes in cycles like this. As predator populations increase, caterpillar populations decrease. When there are fewer caterpillars, prey populations start to decrease. This is followed by an increase in caterpillars.

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Birds eat them, too. While adult birds eat fruit from trees and shrubs, insects are a primary source fed to their young. Caterpillars are a rich source of protein. In the broader scope of nature, insects in general are essential. Plants are the first trophic level to convert sunlight into chemical energy in the form of carbohydrates. Insects are the primary herbivore to consume plants, passing energy up the food chain. Eastern tent caterpillars aren’t just for the birds, but mammals, too. Things like racoons, mice and bats will eat these protein-rich creepy crawlies. From this point of view, having insects around is a good thing.

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If you need to control tent caterpillars, you’ll need to catch them early in their life cycle. If you can remove the nest, problem solved. It will be filled with caterpillars and excrement. Tony Bertauski/Provided

Once we see Eastern tent caterpillars crawling down our driveways or across the hood of a truck, they’re no longer feeding. They just want to find a place in leaf litter or some other dark and secluded place they can call home for about three weeks. Once they’re done pupating, they’ll emerge as moths to mate or possibly get devoured by a bird.

In general, Eastern tent caterpillars won’t kill a tree. Even if they defoliate it, the tree will recover, although this can stress the tree. You’re not likely to see that degree of damage in the landscape. However, if you need to control them, you’ll need to catch them early in their life cycle. Watch for webbing in branch crotches in late winter to early spring. If you can remove the nest, problem solved. The web will be filled with caterpillars and excrement. If that’s too gross, an insecticide can be used. A very safe product is Bacillus thuringiensis var. kurstaki, otherwise known as Bt. This bacterial protein is toxic only to caterpillars.

The caterpillars are protected in the web. Apply product to foliage around it where they’ll consume it when emerging at night to feed.

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