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What’s Eating My Tree? Bagworms or Webworms?

Have you noticed the large webbed sacs in the trees along the sides of the road lately? They do prompt questions to the Home & Garden Information Center’s Ask an Expert service. Often they are referred to as bagworms which causes some confusion because bagworms are a different insect.

So what are webworms and bagworms? Will they cause damage to trees? Let’s take a look at them both.

Fall Webworms. Photo: Kelly Oten, North Carolina Forest Service, Bugwood.org

Fall webworm (Hyphantria cunea)

Fall webworms show up every year but their populations can vary in size. Often they are insignificant in number and not too noticeable, but every so often there is a large population. The sacs can be numerous and quite large, leading one to assume they will devour an entire tree’s worth of leaves.

Fall webworm (Hyphantria cunea). Photo: Milan Zubrik, Forest Research Institute – Slovakia, Bugwood.org

But, thankfully, beneficial insects such as parasitoids and predators such as birds, who love to eat the caterpillars, keep populations in check and spraying is not necessary. Granted, the webs are not pleasing to look at. If they are within reach they can be pruned out and destroyed.

Fall webworm facts

Refer to our webpage about fall webworm

Bagworms (Thyridopteryx ephemeraeformis)

By far bagworms are the more destructive of these two insects and need to be managed. They have voracious appetites and devour the needles of evergreens– particularly arborvitaes, junipers, Leyland cypresses, and cedars. We hear the cries of desperate residents wanting to know if the dead areas on their trees will regrow. Unfortunately, that answer is no.

Bagworm facts

Controlling bagworms

Other tent-making caterpillars

There are two more tent-making caterpillars that are sometimes mistakenly referred to as ‘bagworms’. They are eastern and forest tent caterpillars. Both are active in the spring and not in the summer or fall.

By Debra Ricigliano, Lead Horticulturalist, University of Maryland Extension Home and Garden Information Center

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