Land-dwelling leeches can seem like peaceful creatures. But when they’re out for blood, watch out.
An appetite for blood may have prompted displays of startling athleticism, documented in two videos published Thursday by two scientists along with a study in the journal Biotropica. In each a brown column of flesh and muscle, standing atop a green leaf, flails back and forth in search of blood. It is then rolled into a comma, gathering its lower half. Finally, the leech jumps, flying through the air with a kind of wild abandon.
Lean closer, plug your ear: You can almost imagine hearing a tiny “Yahoooooo!”
Mai Fahmy, currently a postdoctoral researcher at Fordham University and a visiting scientist at the American Museum of Natural History, shot the first video in Madagascar in 2017. At the time, she had never heard of the long-standing debate among scientists about whether leeches could jump.
“It takes a few years of studying leeches before you learn about the big debate,” says Michael Tesler, a leech biologist at the Medgar Evers College of the City University of New York and a research fellow at the Natural History Museum. It is co-authored by Dr. Fahmi.
Her 10-second clip, shot on a whim, turned out to be the first recorded visual evidence known to science of leeches jumping.
There have been other claims of jumping leeches. In 1881, biologist Ernst Haeckel visited Sri Lanka and described the behavior: They not only crawled on the ground, he wrote, but could also “jump to reach their prey.”
Scientists have long been skeptical of such anecdotal evidence. In the rainforest, it is common to find leeches unexpectedly high on the body, on the arms, neck, shoulders or even in the eyes. Did the observers find leeches that had fallen from the vegetation and simply assumed that the creatures could jump?
After Dr. Fahmi shared his first video of a leech popping up with others, most recognized the jump immediately. When she and Dr. Tesler analyzed the leech’s movement, they found that it made a twisting motion similar to the movement a cobra makes before it strikes. The gesture looks like a gathering of energy, preparation for what follows – a flight and an uncoordinated, almost slapping landing.
In fact, they found that this particular sequence of movements — coiling, leaping, ending with a belly-flop — is not uncommon among other worm-like organisms that jump, including caterpillars and fly larvae.
The way the leech descends to the forest floor in the 2017 video, with very little apparent control over its landing, seems to be common among these creatures. It’s possible, Dr Tesler said, because larvae, caterpillars and leeches are so light they don’t need a precise landing to avoid injury.
In 2023, Dr. Fahmy was in Madagascar again, and she took out her phone to photograph a pair of leeches on a leaf. Seconds later she saw the same movement again—one of the leeches gathered and rose into the air. She and Dr. Tesler identified the species of leech in both videos as Chtonobdella fallax, a member of a larger family that also occurs in the Seychelles, Southeast Asia and the South Pacific islands.
That Dr. Fahmi was able to capture these videos without much planning suggests that jumping may be a common behavior for some leeches. The researchers hope that other people can come out and film more acrobatic bloodsuckers. It is possible that one of the problems preventing the identification of the jumping leech all these years was the lack of people with cameras.
However, Dr. Fami and Dr. Tessler note that having a large, warm bag of blood nearby can irritate leeches quite a bit. They will start the leech’s version of running, spinning furiously to try and get close to you.
“It can be quite frantic,” Dr. Fahmy said. “And when there’s a lot of leeches, it can be pretty overwhelming in the field to notice that you’re being chased so intensely by so many little guys.”
“They’re booking it,” Dr. Tessler added. “It can be pretty wild.”
