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Why Are There So Many Caterpillars Around? Hint: It's Not Because Of The Winter Storm

Jerry Clayton | Texas Public Radio
Canker Worm on an Oak Tree

TPR's Jerry Clayton recently spoke with Texas A&M Agrilife Extension entomologist Molly Keck about the overabundance of caterpillars in the area this year.

If you've spent any amount of time outside recently, you may have noticed what looks like an invasion of caterpillars. What's going on? Molly Keck is an entomologist with the Texas A&M AgriLife Extension Service.

Jerry Clayton: It seems like there's a lot of caterpillars around this year. What's going on?

Keck: Well, we're seeing this year, for whatever reason, an overload of Canker Worms. And in some pockets, I'm also seeing some Oak Leaf Rollers. But by and large, the worm that is the most common is a Canker Worm. And they're real similar to Oak Leaf Rollers. They kind of repel out of the tree when the wind blows or they get disturbed by a silk strand and then use that as a lifeline to get back up. But they also have a tendency, more than Oak Leaf rollers, to falling off the tree and climb up the houses and crawl into little tiny cracks in the house that just get all over other things.

Clayton: What's the difference between an Oak Leaf Roller and a Canker Worm?

Keck: So the Oak Leaf Rollers are kind of a lime green, real light colored green with a black, dark, hardened head capsule, and the Canker Worms come in two different colors. There's a green color, and then there's a grayish brown color. And that's what I'm seeing the most of. And they inch. So they're also called Inch Worms. In the past, we've seen Oak Leaf Rollers in huge numbers. This year it's Canker Worms.

Clayton: Are the Oak Leaf Rollers detrimental to the oak trees?

Keck: Oak Leaf Rollers generally don't cause any damage to the trees. Canker Worms in super high numbers can defoliate trees. But these are going to be trees that are not mature, really not established oak trees. And both of them prefer oaks, by and large. The best thing to do for either one is just to wait them out. The trees that do get defoliated will leaf back out again.

Clayton: And these caterpillars, they will attach themselves at some point and then they will undergo the process to become whatever they're going to be. Is that correct?

Keck: They will. And they neither one will turn into anything very attractive. So ... if you step on one ... you're not killing anything that's going to become a beautiful butterfly. They just become kind of gray camouflage looking moths and, you know, as many as many caterpillars as we're seeing. I doubt we're going to notice more moths in the later part of the spring or early summer. It's just [that you] notice them in that form for whatever reason. And then the laws just kind of do their own thing.

Clayton: You said you've been seeing a lot. Is there any particular reason you can think of why there seems to be so many of them?

Keck: A lot of people want to attribute their population increase to the cold weather, and I think that's just a coincidence. I really don't think that there's a link there. It might be because there's just a lot of pollen and a lot of fresh new leaves. And so there's more food for them. And when there's a lot more food, the babies all survive. So that could play a role. But I think we were going to see this happen this year no matter what the weather was like in the wintertime. I think this is just the year they decided to be numerous.

Clayton: And I guess this dispels any thoughts that the major freeze had an adverse effect on insects. They seem to be doing just fine.

Keck: They definitely are. That's definitely a question a lot of people have called and asked about. And unfortunately, insects have so many different defense mechanisms to overcome cold weather. They either hunker down and hide somewhere where it doesn't freeze there in a life form over the winter time. That just doesn't get cold enough like a pupa, where it's ... a little case and it's insulated. Or they also have things in their body, chemicals in their body that act like antifreeze. So there's all these adaptations that they have, unless it's a really tropical species. Entomologists as a group, we've all actually talked about this quite a bit. We really don't think that that freeze that happened over February played any major impact on any insect populations.

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Jerry Clayton can be reached at jerry@tpr.org or on Twitter at @jerryclayton.