A New Species of Blood-Sucking Leech Found In North America for First Time Since 1975

Researchers have identified a new species of leech that has lived in the wetlands of North America for decades.
Donna Fuscaldo
Medicinal leech Photocrea/iStock

A new species of leech has been discovered in the swamp waters of Maryland, the first blood-sucking leech identified in North American since 1975. 

An international team of scientists from the Universidad Nacional Autónoma de México and the Royal Ontario Museum, led by Anna Phillips the curator of parasitic worms for the Smithsonian's National Museum of National History, discovered the new species of medicinal leech called Marcobdella mimicus first in Southern Maryland, less than fifty miles away from Washington D.C.


New species of leech has lived with us for decades 

That discovery led the scientists to collect more samples and examine ones held at the Smithsonian, concluding wetlands from Georgia to New York are home to this new species of leech. Leeches that feed on humans are considered medicinal. Most of the blood-sucking leeches in North America came from Europe. 

"We found a new species of medicinal leech less than 50 miles from the National Museum of Natural History -- one of the world's largest libraries of biodiversity," Phillips said in a research paper published in the Journal of Parasitology. "A discovery like this makes clear just how much diversity is out there remaining to be discovered and documented, even right under scientists' noses."

Leech found from Georgia to Long Island

For years the researchers have been studying the different types of medicinal leeches located in North America. Upon return from collecting leeches from the Maryland swamp back in 2015, the team realized the species didn't match M. decora, the type of leech they thought it belonged to.

Not only did the DNA differ but there was also physical differences when examined close up. The new leeches had multiple reproductive pores along the bottom part of their bodies called gonopores as well as accessory pores, which is found in all leeches. But the pores were located in a different position than the M. decora.  

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The researchers then collected leeches from South Carolina and other places which shared the same DNA. Studying the leeches as well as the parasite collection at the Smithsonian, Phillips said she started finding the new species everywhere from northern Georgia to Long Island.  

Phillps also concluded based on the historical record from the museums' collections, which contain specimens spanning 63 years, the new species of leech was not introduced recently. Nor does it represent a newly evolved species.  The oldest is more than 80 years old.  "It's been here this whole time," Phillips said. "We just hadn't looked at it in this new way."

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