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Fall Galls with Sam Guida

Fall galls

Heidi Holtan:
On Tuesday mornings, we get a little more connected to nature and to some of the changing things out there. And John, you tell me that I might start seeing some of those green or little balls on leaves or on the ground now, right?

John Latimer:
Yeah, that's right: now that the leaves are off of the trees. There are several species of wasps and other small midges and insects that have the ability to force the plant into growing a home for their little egg. Sam will tell us more, but the egg and its larva are the precursors of the fly or wasp that will come out next year and do the same thing again. And, as you're out raking leaves, you might find the odd oak leaf with a gall on it. But boy, they're going to be everywhere. The black ash, the rose, many species of willows, the golden rods: many of them are going to have these swellings, these structures that are homes to small critters.

Heidi Holtan:
Home for maggots, huh?

John Latimer:
Yeah. Home for maggots.

Heidi Holtan:
Sam Guida is back with us this morning. Good morning, Sam.

Sam Guida:
Good morning. Thanks for having me on today.

John Latimer:
Yeah, well it's that time of year! A lot of people have successfully ignored <laugh> all of the little structures that are going on around them because there were leaves to look at. It happens with bird nests as well. This is always the time of year when I'm a little bit embarrassed at my observational skills. I'll walk up to a bush that up until now has been covered in leaves, and now that the leaves are down, I see that there's been a bird nest there all summer and I've just successfully ignored it. But galls are a little harder to find, and now that the leaves are falling they are becoming much more obvious. I want to start this morning with what I consider one of the 'speed limit' sort of galls that you can see. And that is the one on the black ash. That is not actually formed by a wasp, it's a different animal. But when the leaves are down off of the ash, we are left with these clusters of dark brown structures that are hard to miss. Even at 60-70 miles an hour, you'll see this big ash tree as you're driving along and it'll have all of these fist-size dark brown clumps stuck up in it in its branches. And those are the homes for what?

Sam Guida:
Yeah. Wow. They're such a cool, really unique gall. There are homes to small colonies of hundreds or even thousands of microscopic gall mites. If you look at 'em underneath the microscope, they look like tiny little spiders. However, they can't make silk or anything like that, because they're a mite instead of a true spider. But they're in the arachnid family. Early in the spring, they crawl out of the buds in the bark crevices that they overwinter in. This is pretty impressive because they're very, very small, tiny creatures. They don't really move around too much in the winter, and it gets pretty cold out there. But they're still able to survive, and then they crawl out onto these little flower buds and they start feeding on them. And over the course of the summer, it makes these really large lumpy-like green structures.

But just like you were saying earlier, the green generally blends in with the leaves. And if you're not looking really carefully, it's easy to walk by 'em until all the leaves fall down or you've got that beautiful golden color the black ashes turn. And then, as you're driving along or walking, you see the big clusters all of a sudden. They're really unique, and I definitely recommend that as people are driving past the swamps and everything, just to look around. Or, if you have an ash in your yard, they can be found on green ash, white ash, or black ash. They've spread out all over the state, and they're a native, natural organism. They're really fun to look at, especially if you get 'em up close, they look a little bit like broccoli, just brown.

John Latimer:
Yeah, yeah, I agree. Tell me now, are these little mites living in those structures or are they retreating to the bark of the tree?

Sam Guida:
Yeah, they live in those structures. They make the galls all summer and even into the fall. But as soon as the tree starts to drop all its leaves and it gets cold, they leave the structure and return back to inside the bud scales. But you can almost think of 'em as an apartment building or a condominium with a large community of thriving mites just hanging out in them all summer.

John Latimer:
Cool. Now is it just me, or do these mites only attack the male flowers?

Sam Guida:
I haven't looked super closely, but I'm pretty sure you're right. Most of the time, it seems like they really prefer the male flowers and they'll generally just cause the majority of the male flowers to turn. It seems like some trees are much more susceptible than others. I would guess there's some sort of genetic component. It'd be really interesting to know more, but on some very specific trees, you'll be able to find a flower gall with a few little bits of seeds forming underneath: so, they were female flowers.

John Latimer:
Oh, okay.

Sam Guida:
It seems to be much more uncommon. Those [female gall-bearing trees] seem to happen also whenever you have a whole bunch of really affected plants around them. The mites just move over a little bit and they'll take more flowers. Maybe they've run outta space.

John Latimer:
Okay. So my personal experience has been mostly males. So that people understand, the ash. is dioecious, so you have a tree with male flowers and a separate tree with female flowers. And my observations are that usually it's the male trees that have these galls in them and the female trees seem to escape it, at least where I am watching them. So interesting. Well, let's not spend too much time with the black ash, because there's so much more to cover. You can pick where we go from here. But there are roses, goldenrods, willows... It seems like everybody has a partner, <laugh> a predator that creates galls on it.

Sam Guida:
Yeah, it's really interesting because most galls are considered parasites, but they're really good parasites in the fact they don't really end up harming the plant very much. They take very little nutrients out of it. And so, even though they are a parasite, they're not something like you'd expect. A tapeworm or something does a lot more damage over the long run, especially since a lot of [the gall-creating insects] are seasonal. But most plants do have a very specific gall-inducing organism on them that you can only find on that plant (and, often, only on that part of the plant). One that a lot of people start seeing right now as they're out raking the leaves are these weird little round balls that are kind of brownish that you find underneath oak trees. There are a couple of different species of those, and they're called oak apple gall wasps. Have you come across any before?

John Latimer:
I have seen those. Now, some are attached to leaves, and others fall off the tree at various times. My sister-in-law came across some of these oak apple galls that were laying on the ground and brought one home to cut it in half. And I admire her for that. She looked inside to see what was in there and it looked a bit fruit-like.

Sam Guida:
Yeah, there are a couple of different species we often find here in northern Minnesota. One of the most common ones is called the spongy oak apple gall wasp. That one, you really, really have to cut it open to be able to differentiate the different species. But when you slice it open, it looks almost fruit, and it's kind of got this weird orange, brown, foamy, spongy texture inside. In the very center is a little chamber where a tiny wasp lives. And the other one that you often find right now is the larger empty oak apple gall wasp. And they're the same round, brown ball. And when you slice 'em in half, instead of being filled with this foam material, they have all of these tiny spokes radiating out from the chamber in the center.

John Latimer:
Those really cool. One of the things that I read years and years ago was that oftentimes the wasp that creates this gall is not alone in occupying the gall. There are enemies of those wasps that recognize that as a place where they can put their own offspring, and the results are not always good for the original inhabitants.

Sam Guida:
Yeah, you're totally right. A lot of galls have incline species on them which is another gall wasp. And once you start looking closer and closer at our world, the food chain gets more and more complex the smaller down you go. Just as a lot of gall-inducing organisms have to have a specific part of a specific plant to make their gall on it, there are even more hyper-parasitic wasps (meaning a parasite of a parasite). They're roughly the size of a pencil lead when you break it off. They fly around through the world looking for a gall on this plant, and they'll find them and lay their eggs in them. And then you get the scary bug world, where the little parasitic wasp keeps the other insect alive as they eat them. And then, once they finally eat all the less nutritious parts, they'll eat the most important ones and the original host of the goal will die. And this new parasite living in the gall will be able to survive in this new safe home and grow and mature into another wasp to fly away and find a new goal.

John Latimer:
<laugh> But not the one that made the gall to begin with! <laugh> Amazing. I was reading in Donald's Stokes books about nature, and he was talking about the willow pine cone gall. I think scientists at one point had begun doing a study of these things, tore them apart, and found 50-some hyper-parasitic wasp species that came into these galls to exploit the original occupant.

Sam Guida:
Which is super wild when you think about it. And it's really cool. It's also really interesting the deeper and deeper you get into galls. You'll find some, especially on roses, that started out as the initial gall, and then you'll have some sort of parasite come in. Then, hyper-parasitoid eats the initial gall inducer, and then they keep feeding on the gall and they change how it grows. And so you'll find a gall that can only be created by having two different organisms feed on the plant.

John Latimer:
Wow. Talk a little bit about that rose gall because I think a lot of people are sort of attracted to the roses because of the big bright red rose hips. So, they start looking at them, and then they find this big swelling that is usually covered in pricks. And that's essentially what you're talking about. Describe it a little bit and then talk a little bit more about this hyper-parasitic <laugh> community alters it.

Sam Guida:
Yeah. The one I'm talking about doesn't have a common name that's used very often, which is pretty interesting because we all see it all the time as we're wandering out in the woods. I see 'em a lot when I'm out deer hunting or out doing late fall plant surveys. I like to call them the prickly stem gall wasp cuz it's a wasp that lays a bunch of tiny little eggs on roses (especially on prickly wild rose and prairie rose, which you can find all over Minnesota). It gets this really big lumpy burr-type thing in the middle of the stem of the rose, and all of the little wasps overwinter there. In late spring around maple syrup season, as everything starts to thaw, you can actually clip those off of the rose, bring 'em inside, and put 'em in a little covered container and watch it for a few weeks to a few months. And generally, you'll get all of these tiny little wasps that hatch out, and it's really interesting to look at them.

John Latimer:
Yeah. I should say the one gall that I think most people are most familiar with is the goldenrod gall. And maybe we should talk a little bit about that one. First of all, I know from reading and from cutting open a few of these things that these little maggots that live in there excavate their escape route before they go through pupation and become the wasp. Is that common among other of these wasps as well? Do they all have to do this chewing while they're maggots before they become wasps?

Sam Guida:
Ooh, that's a great question. I haven't looked into that too much

John Latimer:
<laugh>

Sam Guida:
The goldenrod gall flies do seem to chew their way out, and I'm not sure if it's harder for them as an adult form without strong mouth parts to get out or if the eggs get laid on the edge, then the larvae chew their way in and enlarge that tunnel they came in on to get out. But it seems like a lot of 'em do start getting their way out right before they pupate over the winter. But there are a large number of midges that cause galls and don't actually overwinter. They'll chew their way out and drop into the soil and pupate in the soil. So, if you have a midge gall, it'll often have little orange larvae in it, or, late in the summer, you'll see a little exit hole where that little tiny larva has chewed its way out, and it's no longer in the gall.

John Latimer:
Wow. Okay. That's cool. I did not know that. The goldenrod galls are sort of species-specific. Canada and Tall goldenrods seem to be their choices. Do we know whether other galls are species-specific? Like you talked about the rose gall, and you mentioned two different roses there. Are they sort of like, "Oh, it's a rose, that's okay." Or are they like, "Oh that's the spiny or spiky rose and that's the one we like?"

Sam Guida:
The simple answer is yes, but when you get a little bit further into it, there are a lot of gall-inducing organisms that are really, really, really host specific and they'll only choose one species of plants that they can live on, and then they'll only choose the bud of a red oak, and that's the only type of plant they can live on. But there are also some, like that rose one we were talking about earlier, or the one you see on the black ash, where they're okay in the really close family of native species such as a couple of different roses or a couple of different ashes. They'll be found on those similar spots on those same similar species instead of just one very specific species. But there are quite a few that you can only find on a certain species of plant.

John Latimer:
Cool. Sam, I want to thank you for joining us this morning. It's always a pleasure to talk to you. Before you go, what is the most spectacular, or what is your favorite gall?

Sam Guida:
Oooh. My favorite gall happens to have a really, really long common name. I really like it because of the long common name as well as how easy it is to find. And that is the Eastern American alder tongue gall fungus gall.

John Latimer:
Whoa.

Sam Guida:
I'll say it once more because it's kind of a mouthful. It's the Eastern American alder tongue gall fungus gall. <laugh>. And so if you're looking at the alders down in the swamps, they form these really large growths. They start green and pink in the spring, but by now they're these black tongue-shaped growths coming out of the little pseudo-pinecones. And they hang on for years.

John Latimer:
Wow. Okay.

Sam Guida:
They're caused by a fungus that infects one of the tiny little branches of the pinecone and causes it to grow probably hundreds of times the length that it's supposed to. They grow into these big twirly masses, and they look really pretty, especially on the snow.

John Latimer:
I have seen those and just ignored them. And now, I am going to check them out.

Heidi Holtan:
Hold on one second! Sam, we just got a text from someone. Mike says, "My grandpa taught me how to collect golden rod gulls and cut them open for ice fishing bait."

Sam Guida:
<laugh>. Yeah, they're a really great bait source as well as lots of chickadees use them. They're really wild because we don't quite fully understand how they produce enough antifreeze to keep the little tiny insects from freezing, especially with how little they move in the winter. But they're there all winter, and you can either cut 'em open for ice fishing bait, cuz they look pretty similar to wax worms, or if you watch a bunch of chickies or nut hatches, they'll pull 'em out in the winter. Or, you can pick 'em in late spring and put 'em in a closed jar and watch the flies hatch out cause they've got really pretty interesting wings. Or you might get lucky and accidentally grow out a hyper-parasitoid.

John Latimer:
Oh, thank you, Sam, thanks so much for joining us. I know there are a lot of students out there who are gonna be grabbing some galls to see what comes out. Can you do that in the fall? Can you bring them in the fall, or do they need to freeze before they can pupate?

Sam Guida:
A lot of them seem pretty similar to seeds that you find. They naturally have a life cycle where they expect to go pretty dormant, and they need the cold weather to fully complete their life cycle. I've tried bringing a few golden rod galls in early, and I (at one point) got one to hatch out. But that'd generally be a genetic anomaly, cuz if you hatch out before your host plant is thriving, you're not gonna be able to find it to lay your eggs on it. So they seem like they do need that cold weather.

John Latimer:
All right. Well, thank you, Sam. That was just a wonderful interview. Thanks so much for joining us.

Sam Guida:
Thanks for having me on.

Heidi Holtan has worked at KAXE/KBXE for over 22 years. She currently helms the Morning Show as News and Public Affairs Director where she manages producers, hosts local interviews and programs, oversees and manages web stories and establishes focus areas of programming like phenology, clean energy, Indigenous voices, Strong Women, local foods, clean energy, economic development and more. Heidi is a regional correspondent for WDSE/WRPT's Duluth Public Television’s Almanac North. In 2018 Heidi received the “Building Bridges in Media” award from the Islamic Resource Group for her work on KAXE/KBXE hosting conversations about anti-Muslim movements in rural Minnesota. During the pandemic, Heidi hosted 14 months of a weekly statewide conversation on COVID-19 for the AMPERS network.
As a mail carrier in rural Grand Rapids, Minn., for 35 years, John Latimer put his own stamp on a career that delivered more than letters. Indeed, while driving the hundred-mile round-trip daily route, he passed the time by observing and recording seasonal changes in nature, learning everything he could about the area’s weather, plants and animals, and becoming the go-to guy who could answer customers’ questions about what they were seeing in the environment.
Sarah Mitchell (she/they) joined the KAXE team in February of 2022. Sarah creates the Season Watch Newsletter, writes segment summaries for the website, and coordinates our Engaging Minnesotans with Phenology project. With a background in wildlife biology, Sarah enjoys learning a little bit about everything, whether it's plants, mushrooms, aquatic invertebrates, or the short-tailed shrew (did you know they can echolocate?).