Why Caterpillars Matter + A Spotted Lanternfly Update

Adam Baker, technical advisor with the Davey Institute discusses all things caterpillars, including their benefit and specific species like the hickory horn devil, bagworm and monarch. Adam also shares the silver lining of the spotted lanternfly invasion hitting the East Coast.

In this episode we cover:  

• Most common caterpillars during each season (1:08)
• Is the hickory horn devil harmful? (3:00)
• Which butterflies are harmful to pawpaw trees (4:00)
• Benefits of caterpillars (5:01)
• Can caterpillars damage your trees (5:57)
• Bagworms (8:18)
• Fall web worm (11:00)
• Understanding bugs in the cycle of nature (12:11)
• How Adam became an entomologist (14:10)(19:51)
• How the monarch butterfly is doing (16:10)
• The spotted lanternfly silver lining (17:53)

To find your local Davey office, check out our find a local office page to search by zip code.  

To learn more about bagworms read our blog, Bagworms: Are They Harmful and How specific Can I Get Rid of Them?

To learn more about Adam's research with the monarch butterflies check out his article with  Maplegrove Magazine.

Connect with Davey Tree on social media:
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Facebook: @DaveyTree
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LinkedIn: The Davey Tree Expert Company 

Connect with Doug Oster at www.dougoster.com. 

Have topics you'd like us to cover on the podcast? Email us at podcasts@davey.com. We want to hear from you!

Transcript

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Doug Oster: Welcome to the Davey Tree Expert Company's podcast, Talking Trees. I'm your host, Doug Oster. Each week, our expert arborists share advice on seasonal tree care, how to make your trees thrive, arborists' favorite trees, and much, much more. Tune in every Thursday to learn more because here at the Talking Trees podcast, we know trees are the answer. I'm joined today by Adam Baker. He's a research entomologist for the Davey Institute based in Kent, Ohio. Today we're talking all about caterpillars. Adam, there's good caterpillars, bad caterpillars, and ugly caterpillars. Is that right? [chuckles].

Adam Baker: Yes. That's right. I think ugly is in the eye of the beholder, but we'll talk about certainly some interesting and eerie alien-like caterpillars today.

Doug Oster: those weird-looking ones, I don't think are ugly at all. As a home gardener, we see the tomato hornworm all the time, and many people think that one is ugly, but I think that is the coolest-looking caterpillar. Tree-wise, what is the one you hear about most of the time this time of the year?

Adam Baker: If we're talking about sort of the pests, the bad guys of the caterpillar world, we're generally talking about the one to two-inch-long fuzzy caterpillars, things like the spongy moth, which have been active in the last month or so. Looking forward towards the fall, we have things like fall webworm. We've got the eastern tent caterpillars and things like that.

As far as some of our more charismatic type caterpillars and butterflies, we have things like the zebra swallowtail, which feed on our pawpaw trees. Things like our silk moths, like our luna moths, and our cecropia moths, which are feeding on things like ash and cherry, and things like that. Some of my favorites, like I mentioned before, was the zebra swallowtail, which it's host plant's pawpaw. Things like the spicebush swallowtail, which feeds on spicebush and sassafras. What's cool about that one is that it's first several larval instars. It mimics a bird dropping to avoid predation.

Then their last couple instars are the ones that look like those little green snakes with the large yellow eyes. Really cool caterpillar to take a look at. Of course, our large silk moth caterpillars are always really fun to find. Things like luna moths that feed on hickory and walnuts. Cercopias that feed on ash and cherry and poplar. Then the big, hot dog-sized hickory horned devil, or the royal walnut moth, which feeds, of course, on hickory as walnuts, ash, cherries, and the like.

Doug Oster: That hickory horned devil, is that one that can hurt you? If you were to grab it, or I have that wrong?

Adam Baker: That one will not hurt you. It's always a good idea to proceed with caution when it comes to handling caterpillars, especially the farther south you go. Some of them have what they call urticating hairs, which can poke you, sting you, because some rashes. The hickory-horned devil is fairly safe to handle.

Doug Oster: Okay. It's scary looking, right? If you didn't know what it was, you wouldn't want to grab it, is that right?

Adam Baker: Certainly, it looks a little bit intimidating. I said, some of them, the later instars are about the size of a hot dog, have these large, red-looking horn-type appendages on them. They almost remind you of one of those long Chinese dragons that you see in the parades and such.

Doug Oster: I have a lot of those trees that you're talking about, but I don't see much damage. I have got an entire pawpaw forest. I'm going to have to go up there and look around. Is that the only host plant? Is it the same way a milkweed would be for a monarch? What is the caterpillar that likes the pawpaw?

Adam Baker: There's several different caterpillars that get on pawpaw. The zebra swallowtail was the one that I mentioned. It's not exclusive to pawpaw, but that's generally its preferred host plant. Also, things like the eastern tiger swallowtails will use things like pawpaw, but also poplar and cherry. A lot of the tree-related butterflies and moths often have a little bit wider host range than something like a monarch butterfly. Generally, some of our common deciduous trees, cherries, poplars, a lot of the things use oak as well.

Doug Oster: Even though the caterpillar is feeding on the tree, the benefit is we get the beautiful butterfly, right?

Adam Baker: From a human perspective, sure. Being able to enjoy butterflies feeding on our nectar plants and our landscapes is absolutely one benefit. Also, there's a reason why these pollinating insects have so much, so many progeny, and that's because a lot of them are preyed upon. On a sort of a different trophic level, as adults, they act as pollinators and provide and facilitate reproduction of plants, but their larvae often act as a very important food source for things like birds and other arthropods. They are very good for the environment on both the providing food for the food web and as well as creating food for the food web.

Doug Oster: Then when you're thinking of caterpillars-- well, I guess when I'm thinking of caterpillars, I'm thinking of homeowners looking up at a tree and seeing it being defoliated and freaking out. Are there caterpillars that do that?

Adam Baker: Yes, certainly. A lot of the caterpillars that we perceive as beneficial, often their adult, their mothers lay a single egg and then disperse those eggs throughout the environment. You really don't see that concentrated damage. The ones that tend to be pests are the moths generally that lay their eggs in clusters and create large aggregations of feeding. A lot of the web-making caterpillars are really the only ones that because sort of that economic damage, as well as the spongy moth, which of course is an invasive species that can defoliate full forests in years where they have large enough populations.

On a regular cycle, our native insects, things like forest tent caterpillar, fall webworm, and eastern tent caterpillar can sometimes reach population levels where they because damage. One sort of interesting story about a pest caterpillar causing unforeseen damage is in Kentucky a few years ago, where they had something called mare reproductive loss syndrome, where there was a bunch of cases where mares were losing their foals before they were born.

The entomologists went to work at it, and that year there had been a very large population of eastern tent caterpillar, which of course loves to feed on things like black cherry, a very common hedgerow tree in Kentucky. What they figured out was that all of those large aggregations were defoliating the black cherries and the hedgerows. They were crawling off of the trees and then moving to find another food source. As they were moving, they were moving through horse pastures, and the mares were eating the caterpillars, and those urticating hairs came off the caterpillars and caused problems in the reproductive system. We're losing very valuable high-stock horses to an exasperated population of eastern tent caterpillar.

Doug Oster: Does bagworm come into this as caterpillars or bagworm is something different?

Adam Baker: Bagworm is definitely a caterpillar. That is one that I missed on my list, so thank you for bringing that one up. [chuckles]

Doug Oster: Explain what the bagworm is, what it looks like, and what we're supposed to do about it.

Adam Baker: The bagworm is an interesting pest. They generally like to feed on things like conifers, but certainly, you'll find them on birch and other type of species. What they do that's interesting is that they'll go around and collect material from their surrounding plants. They'll mix it with silk and create a bag-like structure in which they can live in. This protects them from predators, this protects them from parasitoids, and the elements as well.

What's interesting about these is that the females are wingless and almost resemble a larva, even when they're an adult. The females will feed closely around the bag, and at some point, they will stay in the bag and create a pheromone in which the winged males can then locate them, and they will actually breed there and then create a bunch of eggs for the next season.

After those are overwintered, those tiny caterpillars will emerge from the bags. They do what's called ballooning, where they'll create a thin line of silk. Because their body is so light, and because of that fine silk strand, they'll actually float off into the air like a balloon, finding new host sources in which they can feed.

Doug Oster: If we have those, what we identify as the bag on the tree, that's a bad thing or that's okay, or it depends on how many are on there?

Adam Baker: Sure. Generally, a couple bags probably aren't going to cause problems, but one thing you can do, especially if they're on plants that you've invested in your landscape and are part of your ornamental landscape, is you can simply start removing the bags by hand and discard those in plastic bag or somewhere away from the plant material they're trying to protect. If they do get into bad enough situations and you do want to pursue treatment, I would suggest using something like a natural derived pesticide, something like Bacillus thuringiensis or BT, which will only affect caterpillars and will not mess with all the natural enemies, the predators and parasitoids on your plants that are doing some pest control for you.

Doug Oster: That's an interesting point to basically target the pest with letting the whole cycle of nature continue. That's definitely a good thing. Now, how about fall webworm? You mentioned that, and I'm just guessing that's those ones I see, like if I look in the forest, in the trees, it looks like a big webby nest. Is that a fall webworm?

Adam Baker: Fall webworm is going to be a smaller caterpillar with white hairs. How you distinguish fall webworm and there's a couple of them that are similar things like mimosa webworm and such that behave the same way. The one key thing here is that they build their webs at the tips of branches, and they're often quite smaller than things like the eastern tent caterpillar or the forest caterpillar.

The eastern tent caterpillar usually builds their nests in the fork of branches, whereas things like fall webworm will be at the tip of the branches. Oftentimes, there's not enough caterpillars to really cause cosmetic damage unless you have multiple nests per tree. To address something like these, you can also use something like BT, but you can also use something even easier like a pole pruner, and just prune out those single nests and get those out of there if they are starting to cause some damage.

Doug Oster: As an entomologist, do you see this trend that I think I see, we're bug phobic where in much of what you're talking about here, it is just a cycle of nature and just seeing a bug or a fall webworm or something like that on your tree doesn't necessarily mean that it has to be treated.

Adam Baker: Correct. I think there's certainly a change in culture here in the last several years where we're getting away from this completely clean aesthetic version of our outside landscape for moving into planting more native plants, more plants that are going to be less pest prone, things that have natural resistance to the natural diseases happening. I think in this day and age that maybe seeing a few nibbles on your ornamental plants is a good thing because it says that your backyard isn't sterile, that it's providing ecological function to your landscape or a thing. There's a full cycle going on from pollination to the predator and parasitoid complexes in our backyards. It's exciting in a way that connects us to nature. Moving forward, I think we need to see a lot more of that.

Doug Oster: Do you get a lot of questions from friends and neighbors and maybe even colleagues where they send you a picture of something that they're really afraid of and you tell them that's a firefly? [laughs]

Adam Baker: Yes. If you have any interest in pursuing a career in entomology, you're going to feel like a cryptozoologist because every day I get pictures from friends and family that are always blurry of some random [laughs] arthropod in their yard, but it's a lot of fun. Oftentimes, people are pretty excited to hear all these very intricate and beautiful life history stories of these insects that they're just completely unaware of.

Doug Oster: How did this become your thing to tell me the journey about being an entomologist?

Adam Baker: Sure. I grew up in southwest Michigan and our family live-- our backyard was essentially a bog. I spent most of my time out there catching tadpoles and turtles and water bugs and beetles and stuff like that. That fostered my interest in nature and always as a kid, I wanted to become a naturalist. Eventually, along the lines interests changed a little bit and when I went to to college, I was actually pursuing a degree in environmental literature and nature writing. At which point I took a few entomology classes and changed my directory from there, where those were very interesting to me.

I got some jobs as an undergraduate looking at various entomological things. My first job there was looking at benthic invertebrates where we did stream sampling to understand how dying hemlock in Eastern Appalachia could influence the changes in stream diversity as those streams now transition to deciduous forests. After that, I took a job in a pollinator lab where we were putting together pollinator community data, looking at 75 woody ornamental species in our urban landscapes, and trying to understand how attractive these plants were.

Beyond that, I moved into a PhD position, looking at monarch butterfly conservation, using ecology-based theory to help design habitats and optimize the return and reward for creating these types of habitats, increasing the amount of egg laying going on while still maintaining the same predator predation levels.

Doug Oster: I want to go off-topic a little bit here and start off with monarchs. In general, do we know how the monarch is doing?

Adam Baker: Yes. We have a annual census that happens where Monarch Watch and others help with that effort, where essentially what they do is they use aerial photos of the overwintering grounds each year. There's about 12 discreet locations that they use every year where they congregate by the hundreds of thousands. Essentially, they measure the area occupied by monarch butterflies.

Every year we get a starting point for the population which can be an indicator for growing populations, but of course, the monarch butterfly fluctuates a lot in its population. We have that starting point, but understanding it throughout the season. There's still a lot of things you can do. Various projects like Journey North where you can report sightings of everything from the eggs to the adults to help track populations throughout.

In general, the monarch butterfly is doing okay. It's not at the level that we want it to be. We want it to be sitting at that 6-hectare overwintering mark, which is, we believe the area at which things like a devastating storm or an unknown disease or something that can hit them and they can still rebound. Right now, I think they're about two and a half at the last reading. We're a little bit ways, but with all the programs, the plant milkweed, and all the monarch health stuff going on, I think there's hope.

Doug Oster: Since I have such an expert in front of me, I've got to throw in something about spotted lanternfly because on our side of the region, we are inundated with spotted lanternfly and it is driving people crazy. Are you concerned about this? Have you seen it yet? Are you looking at what might be coming your way?

Adam Baker: You've got it a little bit worse than we do. We don't have it quite yet here in Northeast Ohio, but it's only a matter of time before it shows up here. I have some family that lives on the East Coast in Baltimore, and certainly, it's all over out there. The silver lining with the spotted lanternfly is that it is moving a lot slower than the initial predictions and it's causing a lot less overall tree death than they anticipated. It tends to target trees that are very, very vigorous and healthy unlike some other sucking insect pests that have a pump that can pull fluids out of the vascular system of the tree.

The spotted lanternfly depends on the positive pressure of the tree to push sap into their feeding system. I'm sure you've heard, mention of them, liking things like tree of heaven. At first, it was expected that that may be part of their life cycle being as it is from the same region that they come from, but now it's more believed that just because the tree is so vigorous, it's targeted because of that reason, that feeding reason and because it's so ubiquitous in these disturbed areas where the spotted lanternfly is also at.

Doug Oster: Before I let you go, just tell me a little bit about what you get out of your job. What do you love about your job as an entomologist and helping people identify and deal with these caterpillars and other insects?

Adam Baker: Sure. I think one of the most rewarding parts is how completely diverse the job is. We're not just dealing with pests and solving problems on that, we're also dealing with solutions to mitigate risk to things like pollinators and mitigate risk to other natural insects. One day we may be looking at-- For instance, one thing we're working on right now is we're creating clay caterpillar models that look like little monarchs, and we go pin them to plants all over the place, and then things attack them. As they attack them they leave indentions on the clay caterpillar. Then we can collect them back up, we can look at the indentions, we can assess what species of bird it was, whether it was a wasp, so cool things like that. The ecology is this vast nebulous of connections that some of them that we can see, some of them are unforeseen, but it's the mystery of sort of getting involved with those ecological mysteries that make a really interesting job.

Doug Oster: Adam, that was absolutely fascinating. I really appreciate your time, and I'm sure we'll talk again because I could go another hour with questions about insects. Thanks for your time.

Adam Baker: Thank you very much, Doug. I appreciate you having me on.

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Doug Oster: I hope you're enjoying listening to these podcasts as much as I'm enjoying hosting them. I learn something every time I talk to one of these experts. If you do like what you're hearing, do me a favor, subscribe to the podcast so you'll never miss one of our Thursday Talking Trees podcasts from the Davy Tree Expert Company. I am your host, Doug Oster, and I'd love to hear from you. Send me an email to podcasts@davey.com. That's P-O-D-C-A-S-T-S@D-A-V-E-Y.com. As always, we'd like to remind you on the Talking Trees podcast, trees are the answer.

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