Tent Caterpillar

A tent caterpillar web. The web protects the caterpillars at night and at other times when the insects aren't feeding. 

Tent caterpillars have been showing up everywhere, with large webs this spring in and around Chester County.

Are they dangerous at all, or just unsightly? How do you remove them?

Coordinator of Master Gardeners of Chester County for the local Penn State Extension, Meagan Hopkins-Doerr, answered some questions about the caterpillars to find out what you should know and what you should do about them. She said records on the caterpillars locally date all the way back to 1648.

People keep seeing large amounts of caterpillars in webs in trees around Chester County. What are they?

Tent caterpillars are highly visible in the spring, when they make protective tents or webs on preferred trees. Preferred trees are crabapple trees, apple trees, and cherry trees, including both our native Black Cherry, Prunus serotina, and ornamental flowering cherry trees.

Are they in Lancaster County, too?

Yes, they are. They are across the state.

How large is the region they are found in?

They are found across the continental United States.

What species is in our area?

Eastern tent caterpillars, Malacosoma americanum, emerge from eggs and create tents in the spring. They will feed on leaves for 6-8 weeks before spinning cocoons, and emerging as moths in late June or July. The adults will lay eggs, which overwinter and hatch in the spring.

Sometimes these are confused with fall webworms, Hyphantria cunea, which is another native caterpillar or moth. These caterpillars create tents or webs in the fall on over 90 species but are commonly found on hickory, walnut, birch, cherry, and crabapple trees.

Besides the time of year for visible protective webbing, the two caterpillars place these tents in different areas. The Eastern tent caterpillar webs are formed at the fork of major branches and or the tree trunk. Fall webworm webs are formed at the ends of branches.

Tent Caterpillar Graph

A graphic showing the different types of webs different tent caterpillars make.

So you mentioned this but they are native to the area, correct?

I should say that we believe that they are native. We have records that go back to 1648 about them.

Are they harmful?

No.

What is the purpose of large webs?

The webs protect the caterpillars, mainly at night but also at other times when they aren’t feeding. They will leave the webs to feed on the leaves and then return for protection. As the caterpillars grow, the tent will be enlarged.

What is their place in the ecosystem?

Various birds and other wildlife feed on the caterpillars.

Are there more tent caterpillars some years than others?

Yes. It seems that every seven to ten years, there will be a noticeable increase in the amount of Eastern Tent Caterpillars in a region.

Should people remove them?

That is a more difficult question. We recommend following Integrated Pest Management strategies (IPM). After correctly identifying a pest, the next step is to judge your tolerance levels of the pest. For me, I have Eastern Tent Caterpillars in my yard every year. They temporarily cause aesthetic damage to our black cherry and plum cherry trees but are soon not visible and the leaves grow back.

I appreciate that birds will feed on the caterpillars and feed them to their growing chicks.

I will continue this strategy with my mature trees but if I find Eastern Tent Caterpillars on the sapling American plum, Prunus americana, I will remove them as they do weaken a tree and my young tree may not recover as easily.

If people want to remove them, how should they do it?

The easiest way is to open the netting with a stick so that birds and other predators can easily reach the caterpillars. Some will likely survive but the local population will be greatly reduced.

There are chemical treatment options but those should be applied in April and only to ornamental trees. I have heard of homeowners using more aggressive methods but they risk permanently damaging their trees, which seems overkill for a temporary issue.

What if someone is having trouble identifying the caterpillar or wants to speak with someone directly about them?

That's an easy question. So all of our extension offices have master gardeners who are volunteers with horticultural needs for residents in that county. Each of those Master Gardener groups has a garden hotline that the volunteers will research questions and get back to homeowners with answers about anything related to horticulture from a weird bug they see to a soil question to something with a plant. You can contact your county’s hotline by emailing the county followed by mg @psu.edu so for Chester County that is chestermg@psu.edu.

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