Land-dwelling leeches can appear to be peaceful creatures. But when they come for blood, watch out.
A thirst for blood may have prompted acts of surprising athleticism, as documented in a pair of videos published Thursday by two scientists along with a study in the journal Biotropica. In each, a brown column of flesh and muscle, standing on a green leaf, undulates to and fro on its way through the blood. It then curls into a line and gathers its lower half. Finally, the leech jumps up and flies through the air with a kind of wild abandon.
Lean closer, put your ear to it: You can almost imagine hearing a little “Yahoooooo!”
Mai Fahmy, currently a postdoctoral fellow at Fordham University and a visiting scholar at the American Museum of Natural History, took the first video in Madagascar in 2017. At the time, she had never heard of the long-running debate among scientists about whether the leech could jump.
“It takes a few years of studying leeches to learn about the big debate,” reflected Michael Tessler, a specialist in leech biology at Medgar Evers College of the City University of New York and a research fellow at the Museum of Natural History. It is co-authored by Dr. Fahmy.
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 also been other claims of jumping leeches. In 1881, biologist Ernst Haeckel visited Sri Lanka and described the behavior: Not only did they crawl on the ground, he wrote, but they could also “jump up to reach their prey.”
Scientists have long been skeptical of such anecdotal evidence. In tropical forests, it is common to find leeches unexpectedly high up on the body, on the arms, neck, shoulder, or even in the eyes. Did observers find leeches that had fallen from vegetation and just assumed the creatures could jump?
After Dr. Fahmy shared her first video of the springing leech with other people, most immediately recognized the jump. When she and Dr. Tessler 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 seems to be a gathering of energy, a preparation for what is to come—flight and an uncoordinated, almost grotesque, landing.
In fact, they found that this particular sequence of movements—coil, jump, end with a belly flop—is not uncommon in other worm-like organisms that jump, including caterpillars and fly larvae.
The way the leech in the 2017 video jumps to the forest floor, with very little apparent control over landing, appears to be common among these creatures. It’s possible, Dr. Tessler said, that because larvae, caterpillars and leeches are very light, they don’t need a precise landing to avoid injury.
In 2023, Dr. Fahmy was back in Madagascar and pulled out her phone to film some leeches on a leaf. Within seconds she saw the same movement again – one of the leeches clumped together and lifted into the air. She and Dr. Tessler 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 islands in the South Pacific..
That Dr. Fahmy was able to capture these videos without much planning, suggesting that jumping may be common for some leeches. The researchers hope that more people can go out and film more acrobatic blood-sucking. It is possible that one of the problems that delayed the identification of jumping leeches for all these years was the absence of people with cameras.
Dr. Fahmy and Dr. However, the Tesslers noticed that the presence of a large, warm bag of blood nearby can irritate the leeches quite a bit. They will start the leech version of running, raging worms to try and get close to you.
“It can be pretty frantic,” Dr. Fahmy said. “And when there are a lot of leeches, it can be a little overwhelming in the field to find yourself being chased so intensely by so many little guys.
“They’ll book it,” Dr. Tessler added. “It can be pretty wild.