The Smithsonian Institution

New leech species discovered by scientists in Maryland

A Smithsonian researcher zoologist and her team have discovered a new species of leech in North America for the first time in over 40 years. Anna Phillips, who is also the museum's curator of parasitic worms, led the team as they waded through water to search and collect leeches for analysis. As they ran DNA tests to determine the biodiversity of the leech population, she realized some leeches were different from others they had on record. After closer inspection, and looking through collections of preserved leeches, the team noted there were enough genetic and physical differences that they could consider these leeches a newly discovered species.

According to Smithsonian Magazine, these leeches are "about as long as a cigarette and as wide as two." They're olive-colored, decorated with orange spots, and look remarkably similar to another species of leech. Their nearly identical appearance is the reason they've been dubbed 'mimics' in their new scientific name: Macrobdella mimicus.

With their three jaws, each chock-full of 56-59 teeth, Macrobdella mimicus can drain "two to five times their body weight in blood" due to "expandable pockets in their intestines."

Ian Cook and Megan McCuller/Smithsonian Magazine

"When they swim, they look like ribbons," said Phillips to the Smithsonian Magazine. These types of leeches are also dubbed 'medicinal leeches' because they take blood from humans. Medicinal leeches were once highly desired by doctors during the 18th and 19th centuries to treat illnesses. Some clinics still offer leech therapy treatments today, though its effects and benefits are still being studied.

Phillips is a big fan of leeches, to say the least. She gets excited when she sees a leech, and considers them less harmful than mosquitoes and ticks — insects that can spread harmful diseases like the West Nile virus. She has been eagerly presenting her team's findings at conferences and on social media. One of the greatest parts about this discovery, to her, is how the leeches have gone unnoticed for so long despite being so close by.

"They were overlooked," she said to the Washington Post. "It was unrecognized that these were different."

The team didn't expect to find a new species of leech during their collecting. "Everyone assumed that with the North American medicinal leeches, we knew all that were out there," Phillips explained.

While she was looking through collections of preserved leeches to determine whether this was a new species, she found a specimen of the same type that was found in 1937. This meant that these 'new' leeches have been around for many years, but no one knew it for decades.

"[T]here is unrecognized diversity close to home," quoted Smithsonian Magazine. It's a sign to Phillips, and other nature enthusiasts, that people "don’t have to go very far to find something new."