[MUSIC PLAYING]
SPEAKER: You're listening to Short Wave from NPR.
REGINA BARBER: Hey, Short Wavers. Regina Barber here. And today, I'm joined by producer Hannah Chinn, who's on the pod for the first time.
HANNAH CHINN: Hey, Gina.
BARBER: Welcome.
CHINN: Thank you.
BARBER: They are here to grace our Short Wavers with a story about leeches. And Hannah, to be honest, when I think about leeches, I think about, like, old-timey doctors using them to treat illnesses.
CHINN: Yeah, that's a pretty common conception. There's actually this famous story about someone that you might be familiar with.
MICHAEL TESSLER: I believe that George Washington, when he was dying, had a giant quantity of leeches, like 100, 200, maybe more leeches-- I don't remember-- on him at the time. And that surely didn't help matters.
[LAUGHTER]
TESSLER: Yeah, no, I don't think anybody's gotten better from having 100 or 200 leeches on them.
BARBER: What? Like, I definitely know George Washington. I didn't know this story, though.
CHINN: [LAUGHS] Yeah, well, that's Michael Tessler. He's an evolutionary biologist who specializes in these creepy crawlies, a.k.a. a leech expert.
BARBER: OK, so other than the fact that some of them witnessed the death of our first president, can you just run through some of the basics we know about them for me?
CHINN: Yeah. So there's over 800 known species of these little guys.
BARBER: Wow.
CHINN: But most of them are pretty simple when it comes down to it.
TESSLER: A leech is a worm that feeds on blood, and they do so using strong anticoagulants and slurp up a whole bunch of blood and then often take a long time to digest it.
CHINN: Michael says that leeches are kind of like the vampire cousins of your common earthworm, you know, the kind that you see in your backyard.
BARBER: Wow, OK.
CHINN: And most leeches, not all, drink blood. Some of them actually eat animals.
BARBER: What?
TESSLER: There are nonblood feeding aquatic leeches, ones that eat invertebrate larvae. There are some that come on to land, actually, and eat very large earthworms. Some have frills on their side. Some feed on turtles. Some feed on fish. There's a lot of different things that aquatic leeches can and will do.
BARBER: Cool, cool. So bottom line, overall, leeches are carnivorous worms.
CHINN: Yeah, exactly.
BARBER: Wow.
CHINN: Michael said they range in size from a few millimeters long up to, like, the length of your forearm.
BARBER: That's horrifying.
CHINN: I know. And they're almost everywhere, except for, like, Antarctica. Most of them are in the water. They're aquatic leeches, which make up about 90% of leeches that we know exist. But there are 10% that are not aquatic. They're terrestrial, which means they live on land. And the reason that I want to tell you about them today is because conservation biologist Mai Fahmy accidentally learned new information about them when she was working on her dissertation in Madagascar.
[MUSIC PLAYING]
CHINN: She was collecting leeches to pop in her bag and bring back to study when, suddenly, she got this idea.
MAI FAHMY: One afternoon, I thought it might be fun to, instead of immediately spotting a leech and putting it in a bag, to sort of sit next to it and see how it behaves and what it does, sort of to get myself acquainted with this new study species.
CHINN: And so that's what she did. She found a leech, and she sat down. And she did exactly the same thing that I do when I see a cool thing in the wild. She took out her phone.
FAHMY: I saw this leech on a leaf, and I sat down next to it. I mean, as soon as I took out my phone, in under ten seconds, that leech jumped twice. I thought, well, if it jumped that quickly, surely everyone's seen a leech jump. I really thought nothing of it. And I came back, and I showed my colleagues, my lab mates. They couldn't believe what I had.
CHINN: Mai's work, some of which she's done with Michael, is really changing what we know about terrestrial leeches and their behavior.
BARBER: So today on the show, leeches, they're everywhere, even on land. So what do scientists know about them? What do they still have to learn? And should we be afraid?
CHINN: Gina, don't fearmonger.
BARBER: It's a genuine question that you actually scripted in for me.
CHINN: OK, blame the production team.
BARBER: Yep.
CHINN: [LAUGHS]
BARBER: You're listening to Short Wave from NPR.
BARBER: OK, so we're going to start with a kind of historical retrospective here. Even though land leeches are brand new to me, I guess we've known about them for like a long time.
CHINN: Yeah. Mai actually recounted a very rich history.
FAHMY: For as long as people have been visiting places where they're found or for as long as people have lived alongside them, there are records, historical records, that refer to them.
CHINN: The earliest reference Mai and Michael found dates all the way back to the 14th century.
FAHMY: So quite a ways back, where people have been harassed by these leeches and talked about it in their travel journals. Certainly, the people who live in terrestrial leech territory encounter them pretty regularly and are intimately familiar with their behaviors.
CHINN: And Mai said terrestrial leeches live in rainforests across the Indo-Pacific region, so in Madagascar, in South and Southeast Asia, even Japan, all places where people have lived for a while.
FAHMY: So they are descended from an aquatic ancestor. And we know that they've likely arrived where they are today by latching on to things that move and fly far distances. It's likely that they arrived in Madagascar on things like migratory birds, and likely only took hold after Madagascar moved down to its current latitude.
CHINN: Classic leech stuff-- stick onto a bird or something, hitchhike your way to a rainforest. Leeches don't actually need warmth, which I was surprised about. They mostly just need a lot of healthy forest canopy and a damp environment. So end up in a lush rainforest, decide it's nice, move in.
BARBER: So if I were to go to one of these places, like these rainforests, what would I be looking for? Like, what do these leeches look like? Do they look like an average, like, slug?
FAHMY: They actually come in a surprising variety of colors and patterns, specifically the ones that tend to be found living in shrubs, in greenery. Those tend to be the more colorful variety, presumably to camouflage among the leaves. So you've got terrestrial leeches that have got these bright greens and oranges, white polka dots.
BARBER: OK, I'm not going to lie. This is painting a very like pretty picture. There's these bright colors, lush forests, and these, like, little baby leeches.
CHINN: I know, right? The whole thing sounds pretty cute. And the terrestrial leeches are little.
BARBER: Aw.
CHINN: They're, like, a lot smaller than aquatic leeches.
FAHMY: And they're more tube shaped, whereas aquatic leeches are kind of more flattened in terms of their body plan. So aquatic leeches sort swim in an S curve, and terrestrial leeches seem to inchworm around and jump.
CHINN: And that inch worming is also what sets them apart from worms or slugs. They move way differently.
FAHMY: So an earthworm is sort of like a floppy piece of spaghetti, right, whereas a leech is essentially a tube with two suction cups, one on each end, and they use these suction cups to move. So there's one in the back, and the leech will anchor itself, sort of wave around and then land the front sucker and then unstuck the back sucker and, in that way, sort of inchworm along.
BARBER: Sort of like a slinky, then.
CHINN: Yeah, Yeah, yeah. No, exactly, like a slinky.
BARBER: But, Hannah, I pulled up the video you sent me, like, the one that my Mai. We'll put it in the episode notes, don't worry.
CHINN: Yes.
BARBER: And leeches, they do way more than inchworm along. They jump.
CHINN: Right, which, it turns out, is a big deal. Mai said this is an issue that's been debated among experts for a really long time, like hundreds of years.
BARBER: Wow.
FAHMY: You can go back to Victorian-era times, when leech naturalists were coming on the scene. And a lot of them have conflicting opinions. Some of them are hardcore opposing the notion that any leech can jump at all, that they-- it's not even possible physically for a leech to jump. And then you dig a bit deeper, and you realize that some very early explorers, like Ibn Battuta from the 14th century recording, oh, no, leeches jump. They jump, for sure.
BARBER: It seems so strange that, like, it took scientists so long to like, agree that it jumped when she found it so quickly with this video.
CHINN: Mai mentioned that, actually. She said local communities had really already known this. Like, they've been living alongside leeches for a really long time. They agreed that leeches jump. It's just that scientists--
BARBER: Like Western scientists.
CHINN: Western scientists, yeah, hadn't studied them doing so.
BARBER: Right.
CHINN: And Michael actually weighed in here. He and Mai did work together to study the Madagascar land leech again and release a paper confirming that, like, terrestrial leeches jump.
TESSLER: The rest of leech biologists essentially said, no, this can't be. It's extremely unlikely, if not impossible. Some were willing to concede that maybe leeches that climbed up things would detach their suckers and essentially fall down. But leeches are not weak animals. They-- they're muscular. And they very much, in this case, are using those muscles. I think for both Mai and for me, the video is so obvious. It's so clear what's happening. There's a leech. It jumps, right? It's like, yeah, that leech jumps. People's nightmares are true.
CHINN: People's nightmares are true.
BARBER: Yeah.
CHINN: And I mean, it does kind of feel like the scientific community should have figured this out sooner. But Michael and Mai said there's a lot about terrestrial leeches that we still don't know.
TESSLER: Most invertebrates are painful understudied. Leeches actually get more attention than most because people get grossed out by them, and they're scary.
FAHMY: There's so much mystery, so much we don't yet understand about why they do what they do in terms of their feeding behavior, the way they move, how long they survive, you know, what they're capable of doing or transmitting or teaching us. There's just so many unanswered questions, still.
CHINN: And here's the thing, Gina. Researchers like Mai and Michael are worried that we might never answer those questions if we don't start seriously addressing climate change.
FAHMY: Old, pristine rainforests are unfortunately disappearing globally. They're taking leeches with them. And as we've discussed, we know so little about them, including their diversity overall, their behaviors, their inclinations. That's part of, you know, the biodiversity crisis that we're living through and the effects of climate change that we're witnessing. We're losing what we don't know we have.
CHINN: Researchers estimate that we lost 3.7 million hectares of tropical rainforest last year. That's like 10 soccer fields every minute--
BARBER: Oof.
CHINN: --which is huge on its own, right?
BARBER: Yeah.
CHINN: Like, these forests are important for sucking up and storing carbon dioxide, which otherwise gets released as a greenhouse gas and worsens climate change, right? We don't need that.
BARBER: No, that's so horrifying.
CHINN: But it also means that we could lose all the biodiversity that comes with that forest. Rainforests are home to half the living animal and plant species in the world, and we might never get to learn about those species or how they support the local ecosystem or how they could be helpful to humans, for our human-centric listeners out there.
BARBER: Like me.
CHINN: Like you. [LAUGHS]
BARBER: Hannah, thank you so much for making me care about leeches. I mean, this has been a really fun yet very bloody story. And also welcome to the pod.
CHINN: Thank you so much, Gina. This was a lot of fun.
BARBER: This episode was produced and fact checked by Hannah Chinn. It was edited by showrunner Rebecca Ramirez, and the audio engineer was Maggie Luthar. Beth Donovan is our senior director, and Colin Campbell is our senior vice president of podcasting strategy. I'm Regina Barber. Thank you for listening to Short Wave from NPR.
Copyright © 2024 NPR. All rights reserved. Visit our website terms of use and permissions pages at www.npr.org for further information.
NPR transcripts are created on a rush deadline by an NPR contractor. This text may not be in its final form and may be updated or revised in the future. Accuracy and availability may vary. The authoritative record of NPR’s programming is the audio record.