New Species of Medicinal Leech Discovered

An international team of biologists has discovered and described a new species of medicinal leech living in the freshwater wetlands of the eastern United States. It is the first description of a North American medicinal leech since 1975.

Macrobdella mimicus. Image credit: Ian Cook.

Macrobdella mimicus. Image credit: Ian Cook.

Leeches are parasitic worms, many of which feed on the blood of their hosts.

In the 1700s and 1800s, physicians used leeches to treat a wide range of ailments, believing that by ridding a patient’s body of bad blood, the parasites could cure headaches, fevers and other conditions.

Any leech that readily feeds on humans is considered a medicinal leech, although in North America most leeches used for bloodletting were imported from Europe, leaving native species relatively undisturbed.

“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,” said Dr. Anna Phillips, research zoologist and curator of Clitellata and parasitic worms at the Smithsonian’s National Museum of Natural History.

“A discovery like this makes clear just how much diversity is out there remaining to be discovered and documented, even right under scientists’ noses.”

Dr. Phillips and colleagues found genetic and physical differences that distinguished the new leech, named Macrobdella mimicus, from other species.

“Leeches have multiple reproductive pores along the bottom of their bodies, known as gonopores and accessory pores,” the researchers said.

“In the new leech species, the gonorpores and accessory pores were located in a different position relative to each other.”

The team’s molecular, geographical and morphological data suggest Macrobdella mimicus occupies a sliver of the eastern United States that is nestled between the ranges of two other medicinal leech species.

The historical record from the museums’ collections adds another critical layer of information, confirming that the species was not recently introduced to the area and does not represent a newly evolved species.

“It’s been here this whole time. We just hadn’t looked at it in this new way,” Dr. Phillips said.

A paper describing Macrobdella mimicus was published in the Journal of Parasitology.


Anna J. Phillips et al. 2019. Phylogenetic Position and Description of a New Species of Medicinal Leech from the Eastern United States. J. of Parasitology 105 (4): 587-597; doi: 10.1645/18-119

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