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How To Remove Unsightly Bagworms From Your Trees And Shrubs

Bagworms - shrub & tree pests in PA

Dealing with Tree Pests in PA


It’s an unpleasant name, but then again, bagworms aren’t pleasant creatures.

Despite their name, bagworms aren’t actually worms, but caterpillars that spend their summers feeding on trees and shrubs. The most commonly attacked plants include arborvitae and juniper.

Bagworm larvae cause damage to plants by eating needles and leaves. Older larvae can cause considerable damage, especially those that feed on evergreens.

Where did bagworms come from?

Like many tree pests in PA, they were introduced to our shores accidentally, arriving from Europe in the 1940s and first discovered in Albany, NY in 1962. They have since spread to Pennsylvania and other states in the mid-Atlantic region, and as far west as Nevada.

The bagworm gets its name from the spindle-like silken bags the creatures spin to keep safe from birds and other predators. The bags allow them to blend into a tree, which is good for the bagworms, but bad for you, as it allows them to go undetected until the point that they’ve done a lot of damage.

A year in the life of a bagworm

Bagworms typically hatch in early June, spending their winter inside eggs that rested in their mother’s old nests.

As soon as young larvae hatch, they begin to spin and build their bags as they feed. They enlarge their bags as they grow larger and they attach parts from the plants they feed on for camouflage to help them hide from predators.

Bagworms will reach maturity in late August or early September. By this point, their bags have gotten about two inches long and are impervious to pesticides. They will then affix the bags to tree branches as they begin their transformation into their adult form, black, furry moths with clear wings.

A winged male bagworm adult will then fertilize a wingless female, who lays eggs in the bag. Each female can produce up to 1000 eggs. Those eggs spend the winter in the old bag, hatch in the spring, and the cycle begins again.

How can we control bagworms?

Early detection is key here, for as we noted above, if you don’t notice the infestation in time, the bagworms will be harder to kill with insecticides when they reach a large size.

So start to look for bagworms in the winter or early spring. Their bags, which remain attached to the plants even after the bagworms are gone, are brown and about 1 to 2 ½ inches long. Usually, they’ll be covered with dead needles or leaves. You might even mistake the sacks for pinecones.

It’s possible to simply remove the bags early on – before June when the eggs hatch – and put them in the trash or drop them in a bucket of soapy water to kill them. Pesticides will be most effective if treatment begins early enough in the season when the bagworms are small and mild pesticides can be used. Later in the season when they are larger, harsher pesticides can still be used to try to control them.

The best time to treat for bagworms is during June and early July when they are small and before significant damage has been done to your plants.

Bugged by Bagworms? Willow Tree and Landscape Service Can Help

If you have bagworms – or any other tree pests – bedeviling your property, be sure to contact Willow Tree and Landscape.

We’ve spent more than three decades battling diseases & tree pest infestations while caring for plants in Bucks and Montgomery counties. Our experts can help knock out your infestation and keep your trees healthy.