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Ohio State Professor Says Yellow Springs Webworm Outbreak Nothing To Worry About

Fall webworms (Hyphantria cunea) devour foliage on a black walnut tree south of Yellow Springs. They are greenish-black, hairy caterpillars.
Chris Welter
/
WYSO
Fall webworms (Hyphantria cunea) devour foliage on a black walnut tree south of Yellow Springs.

Joe Boggs says the extraordinary outbreak in and around the Village of Yellow Springs in Greene County has an ecological explanation.

The areas around Yellow Springs have been experiencing an outbreak of fall webworm moths. If you’ve driven in and out of the Village, you may have seen some trees almost completely encased in webs. And, on a windy day, you may have even seen frass, or insect poop, literally falling from the trees.

But fall webworms are native to Ohio—and extraordinary outbreaks like these only happen every once in a while. WYSO Environmental Reporter Chris Welter spoke with entomologist and Ohio State University professor Joe Boggs.

Chris: So, Joe, to start, can you explain a little bit more about what Fall Webworms are?

Joe: Let's start with the fact that these are moth caterpillars. So late in the spring, moths emerge from overwintering pupae and then those moth’s mate, and if they're females, they lay eggs. Once those eggs hatch, then those caterpillars start getting together and constructing a communal nest. That silk helps protect the caterpillars from environmental issues like heavy rain. That's why they're very hairy, because it allows them to hang out in the nest. It keeps them in the silk nest so they don't wash out. Also, predators, birds don't have an easy way to get to these.

Now, the first generation nests can be pretty good sized, but you all may not have noticed many of them in Yellow Springs and that's usually typical. It's only because there aren't that many. However, the moths that matured in those first generation nests, those females will lay their eggs very close to the nests from which they developed. I think you can probably guess where that's heading, Chris. Then the second generation nests get larger because the second generation caterpillars go right back into the same house and they just keep expanding the building. So that's why you're seeing what you're seeing. You're seeing these many, many nests, big nests and entire trees now being enveloped.

Chris: And then from an ecological perspective, what exactly is happening?

Joe: There are something like over 50 different predators and parasitoids and so on that can make a living on fall webworms. So every now and then, in this case, the pest is out producing those things that naturally limit it and we get what we call an outbreak. That's what's happening in Yellow Springs.

Chris:The big concern that I've been hearing from folks in Yellow Springs is if these are harmful to trees?

Joe: Fall Webworms have been with their trees for tens of thousands, hundreds of thousands of years. So whenever you have what we would call a pest with its host tree coevolving, well, I hate to put it, you know, in anthropomorphic terms, but they kind of get along. They learn to get along in a way. The trees, for example, they're able to withstand this type of occasional heavy defoliation and by the time we're seeing what we're seeing right now in Yellow Springs, those trees have already acquired enough carbohydrates to store so they can support leaf expansion next spring.

A tree with a number of fall webworms on its branches.
Chris Welter
A tree with a number of fall webworms on its branches.

I think those who grew up in Yellow Springs or lived there for many, many years probably have never seen anything like this before. It's probably happened before, but it's been so long ago that they just never don't recall it or weren't there or whatever. The point being is that the trees have plenty of time to recover in between these outbreaks. So while it's a real challenge right now, it does look bad, over the long haul on these mature trees, it's probably not going to cause any great harm.

Chris: So if someone has a tree in their yard with these Webworms, what should they do?

Joe: Don't panic. Don't be concerned. Some of those trees are so big that there is very little to do anything about it anyway. So don't don't be overly concerned. It is a nuisance. We call insect excrement frass. Those are little black pellets that fall out of the trees and of course, if you're standing under the tree, much of that's caught in the webbing but still, I was surprised that with a gentle breeze the frass was coming down. So it's a nuisance. But at this stage, really, there's very little that can be done or actually nothing that can be done beyond just remaining patient and also informed that these trees are not going to be hurt over the long haul.

Environmental reporter Chris Welter is a corps member with Report for America, a national service program that places journalists into local newsrooms.