A New Bloodsucking Leech Species Found Hiding Outside Washington, D.C.

Sep 1, 2019
Originally published on September 1, 2019 2:15 pm

With an olive-green body encasing three jaws, each lined with more than 50 teeth, it looks like a cigarette-sized relative of the skin-crawling creature from the Alien films. Actually, it's far less sinister: a new species of a bloodsucking leech.

Anna Phillips, the curator of parasitic worms at the Smithsonian's National Museum of Natural History in Washington, D.C., led the team that recently discovered Macrobdella mimicus in almost their own backyard.

Uncovered in the swamps of Charles County in Maryland, it's the first species of medicinal leech discovered in North America since 1975, Phillips says.

Their superficial likeness to the common species known as Macrobdella decora, found across the northern U.S., has allowed them to go undetected for so long, leading the team to name the new species "mimicus," after the Greek word meaning "imitator."

DNA tests ultimately led the team to identify the leech as a new species. Parasitologists look to the arrangement of pores on the bottom of leeches' bodies to help distinguish species. The researchers noticed a slight discrepancy in the arrangement of the leeches' accessory pores — pores that secrete mucus to allow mating leeches to latch together.

"It's been here this whole time," Phillips said in a press release from the Smithsonian Institution. "We just hadn't looked at it in this new way."

But once the scientists ventured into the new species' native habitat, it didn't take much for Phillips' team to catch the specimens — or rather, for the specimens to catch them.

"Our collection method is to roll up our pants, wear water sandals, and wade in about knee-deep, make a little bit of movement, stir up the vegetation and the mud and — they come to us," Phillips said in an interview with NPR's Weekend Edition.

Phillips says humans shouldn't necessarily fear their bite alone.

But when leeches are harmed — whether yanked, burned or salted — Phillips says, they can regurgitate the bacteria that sits in their intestines to facilitate their digestion into the wound, leading to infection.

Leeches, parasitic worms that feed on the blood of animals and humans, have an ancient history in medical quackery due to the belief that bloodletting helped purge the "tainted" human body of various ailments.

In recent years, however, medicinal leeches are making a comeback in hospitals and scientists' labs.

The anticoagulants found in their saliva can facilitate blood flow, preventing blood clots from forming in damaged tissue. Surgeons also use the critters during reconstructive procedures, such as finger reattachment, to replace stale blood with fresh, leech-drawn, oxygenated blood.

NPR's Peter Breslow and Melissa Gray produced and edited this story for broadcast. Emma Bowman produced this story for Web.

Copyright 2019 NPR. To see more, visit https://www.npr.org.

LEILA FADEL, HOST:

It looks a bit like a very mini version of the creature from the "Alien" movies. It's olive green with three jaws, over 50 teeth, and it sucks blood. It's Macrobdella mimicus, a newly discovered species of leech uncovered in the swamps of Charles County, Md.

Anna Phillips, curator of parasitic worms at the Smithsonian's National Museum of Natural History, led the team that made the discovery. She's in the field and joins us from Connecticut.

Welcome to the program, Anna.

ANNA PHILLIPS: Thanks so much.

FADEL: So tell us about this critter.

PHILLIPS: It's the first time we've described a new medicinal leech species from North America in 40 years. And it has a number of characteristics that make it as a new - considered a new species.

FADEL: What's up with the three jaws? Is this common?

PHILLIPS: Most leeches in this group and other groups have three jaws, but the number of teeth in those jaws is more variable.

FADEL: So why three jaws? What do they need them for?

PHILLIPS: Jaws are held internally, and when they're interested in feeding, they'll spread their mouth out to create a sucker, kind of like a suction cup on a window. And then they push the jaws out. And the jaw - they're muscular and lined with teeth. And they move the jaws back and forth to create the wounds in the teeth. And then that sucker helps suck the blood from the wound.

FADEL: That does not sound comfortable.

PHILLIPS: Really, you don't feel it. I mean, most of the time, you're standing in water; you're surrounded by plants; you're probably not paying attention. And it may feel like a little bit of an itch, if anything, but I can see how it's really unnerving to people to be minding your own business, standing in water, and then look down and find a large bloodsucking worm on you.

FADEL: (Laughter) And that's how you discovered the leech - by getting it to bite you.

PHILLIPS: Well, usually, I try to catch them before they actually bite. And also, you can see them swimming through the water, but sometimes it's inevitable.

FADEL: So what does the leech actually look like? How big is it?

PHILLIPS: It varies in size - maybe an inch long. Some of the largest specimens can be between 6 and 8 inches long. But really, leeches stretch, so it's kind of hard to estimate.

FADEL: So this is the first new find of a medicinal leech in North America since 1975. What is a medicinal leech?

PHILLIPS: So a medicinal leech is a common name that we use for leeches that feed on humans...

FADEL: Oh.

PHILLIPS: ...And have anticoagulants that could be used in modern medicine. Leeches have these anticoagulants in their saliva. So when they bite, that causes the blood to flow and for the blood to stay liquid inside the leech once it's eaten it. And this has been used in medicine for many, many years. It was most popular in the 17, 1800s in Western medicine, and it's even used today in modern medicine. Leeches are approved medical device in the United States, and they're used readily.

FADEL: Tell me about your collection method. How did you find this three-jawed leech?

PHILLIPS: These leeches feed on blood, and they predominantly are probably eating blood of amphibians, for the most part - amphibians and fish and, occasionally, mammals. And whenever a human comes into the swamp, they will feed on them as well.

FADEL: Uh-oh.

PHILLIPS: So our collection method is to roll up our (unintelligible), wear water sandals and wade in about knee-deep, make a little bit of movement, stir up the vegetation in the mud and...

FADEL: That sounds terrifying.

PHILLIPS: (Laughter) It's not for everybody.

FADEL: Anna Phillips of the Smithsonian's National Museum of Natural History. Her team's findings were published in the August 15 issue of the Journal of Parapsychology.

Thanks so much for speaking with us.

PHILLIPS: Thanks for having me. Transcript provided by NPR, Copyright NPR.