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Terrestrial leeches may seem like docile creatures, but when they’re out hunting for blood, you need to be careful.
That thirst for blood may have inspired these remarkable athletic feats, documented in two videos that the scientists published Thursday along with their research paper in Biotropica. In both videos, a column of brown flesh and muscle standing on a green leaf swings back and forth in search of blood. Then it curls its lower body and coils into the shape of a comma. Finally, the leech leaps, flying through the air with almost feral abandon.
If you get closer and put your ear to it, you can almost hear a tiny “Yahoo!”
Mai Fahmi, now a postdoctoral researcher at Fordham University and visiting scientist at the American Museum of Natural History, shot the first video in Madagascar in 2017. At the time, she hadn’t heard of the long-running debate among scientists about whether leeches can jump.
“It takes years of leech study to tell the big story,” recalls Michael Tesler, a leech biology expert at Medgar Evers College, City University of New York, and a research associate at the Natural History Museum, who co-authored the study with Dr. Fahmy.
Her spontaneous 10-second video was the first scientifically documented visual evidence of a leech leaping.
There have been other claims that some leeches jump: in 1881, biologist Ernst Haeckel visited Sri Lanka and described their behavior: “Leeches not only crawl along the ground, but are also able to jump up to approach their prey,” he wrote.
Scientists have long been skeptical of this anecdotal evidence. In tropical forests, leeches are commonly found in unexpected places high on the body, such as the arms, neck, shoulders, and even the eyes. Did observers simply find leeches that had fallen from plants and assume the creatures could jump?
When Dr. Fahmy shared the video of the leech’s leap with others, most of them immediately recognized it. When he and Dr. Tesler analyzed the leech’s movements, they found that the animal engaged in a coiling motion similar to the one a cobra makes before striking, a motion that appears to store energy and prepare for what comes next: flight and a dissonant, almost slapstick, landing.
In fact, they found that this particular sequence – rolling up, jumping, and finally collapsing to the ground on their stomachs – is not uncommon among other jumping insectoids, such as caterpillars and fly larvae.
A 2017 video of the leech plummeting to the forest floor appears to show little control over its landing, but this is likely common among these creatures. Dr Tesler said that because larvae, caterpillars and leeches are so light, they may not need to land precisely to avoid injury.
In 2023, Dr. Fahmy returned to Madagascar and took out her phone to film a pair of leeches on a leaf. A few seconds later, she witnessed the same movement again: one of the leeches curled up and launched into the air. She and Dr. Tesler identified the species of leech seen in both videos as Chtonobdella fallax, one of a larger family that also lives in the Seychelles, Southeast Asia and the South Pacific islands..
The fact that Dr. Fahmy was able to capture these videos without much planning suggests that jumping may be normal behavior for leeches. The researchers hope that others will capture more acrobatic blood-sucking creatures. One problem that has prevented leech jumping for so many years may have been the lack of people with cameras.
However, Dr. Fahmy and Dr. Tesler point out that having a big bag of warm blood nearby can get a leech pretty excited, and it will start scurrying around like an inchworm, frantically trying to get to you.
“It can get quite frantic,” Dr. Fahmy says, “and when you have a lot of leeches, you can get overwhelmed when you’re out in the field, realizing you’re being chased by so many little guys.”
“They book it,” Dr. Tesler added. “It can be pretty wild.”
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