Ancient Leeches Weren’t Bloodsuckers—They Were Way Creepier

437 million years ago, the Midwestern suburb now known as Waukesha County, Wisconsin, was a tropical coastline. It was teeming with trilobites, early scorpions, and other prehistoric creatures.

It was the Silurian period, an era that may have been the birthplace of the first known leech, which was much more of a lethal hunter than the parasitic bloodsucker it is known to be today.

Discovered in the limestone near Waukesha, a creature named Macromyzon siluricus, which means “large sucker from the Silurian,” was a cowbell-shaped sea creature with a segmented body.

It had a big ol’ suction cup on the portion of the body we would scientifically refer to as “the butt,” a feature still found on modern leeches. However, unlike modern vampiric leeches, Macromyzon lived in saltwater and ate large prey.

Ancient Leeches Didn’t Drink Blood—They Did Something Much Creepier

All modern leeches, even the ones that don’t drink blood, carry anticoagulants. But Macromyzon lived in a time and place where vertebrates were rare and hard to poke, as they were all covered in armor.

So instead of bloodsucking, it may have been going full hardcore on trilobites and such by either swallowing them whole or puncturing their softer bits and then sucking out their insides like they were a living Go-Gurt.

The fossil’s preservation can likely be attributed to ancient microbial mats that protected it from millions of years of weather and natural decay. These mats preserved these fossils so well that they offered modern researchers a rare look into a soft-bodied creature that usually dissolves into the earth.

Kenneth Gass of the Milwaukee Public Museum disagrees with the research team’s findings. He argues that previous claims of terrifying ancient leeches in Wisconsin eventually turned out to be other worm-like creatures. Simple mistake.

They’re all ancient gelatinous tubes.  But the study’s lead author, Dr. Danielle de Carle, a leech expert from the University of Toronto, says she knew what they had on their hands right away. Speaking with the New York Times, she said, “This one looked the most leech-like to us,” adding that “the second we saw it, we knew we had something.”

Suppose Macromyzon proves to be the real deal. In that case, it means leeches have not only been lurking around in the United States for over 400 million years, but that they were much more menacing killers than the obnoxious parasites we commonly associate with lawyers today.