Leaping Leeches Caught on Video

by AMNH on

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A small, thin leech stretched out on Mai Fahmy's finger. A leech on lead author Mai Fahmy’s hand in Madagascar’s Ranomafana National Park.
© Mai Fahmy

Personal accounts of jumping leeches have shown up in field notes for more than a century, written by explorers who would encounter these parasites in rain forests. But leech biologists have often argued against these claims, saying it was more likely that the bloodsuckers climbed onboard their prey unnoticed or dropped onto them from vegetation above.

Now, two videos provide evidence that at least one species of terrestrial leech in Madagascar actually can jump. 

“We believe this is the first convincing evidence that leeches can jump and do so with visible energy expenditure,” said Mai Fahmy, a visiting scientist at the Museum and a postdoctoral researcher at Fordham University who is the lead author on a paper about the behavior in the journal Biotropica, out today. 

In 2017, Fahmy was on an expedition in Madagascar’s Ranomafana National Park when she serendipitously recorded a leech from the genus Chtonobdella springing back on a leaf and then leaping. She returned to Madagascar in 2023, this time for fieldwork in the Ivohiboro Protected Area. Once again, she observed a Chtonobdella leech making a motion similar to a “backbending cobra”—or to a spring being pulled back—and jumping to the ground. And once again, Fahmy was filming. 

Mai Fahmy sits at a table wearing a head lamp using a plastic transfer pipette in a brightly colored tray.
Mai Fahmy, the lead author of the new study, processing leech samples in Madagascar’s Ranomafana National Park in 2017.
© Mariah Donohue

As the videos show, the leech keeps its body extended as it soars through the air—a notable departure from their usual inchworm-like movements. “Essentially, it executes a graceful jump but with a seemingly hard landing,” said Michael Tessler, an assistant professor at City University of New York (CUNY)’s Medgar Evans College and a research associate at the Museum who is coauthor of the new study. 

Leeches aren’t the only worm-like animals that can jump. Others include the larvae of gall midges, the larvae of Mediterranean fruit flies, “skipper flies,” and several caterpillars. 

The leaping leech that Fahmy observed on the 2023 trip was collected and identified as Chtonobdella fallax, a common species in Madagascar. Leeches in the Chtonobdella genus are widespread across Madagascar, the Seychelles, the Malay Archipelago, and the South Pacific Islands.

“We do not know how often this may happen or whether these leeches use this ability to seek out hosts, but, given that we caught multiple jumps in two short recordings, this behavior may be common for this species,” said Tessler, who studied leeches extensively as a graduate student in the comparative biology Ph.D. program at the Museum’s Richard Gilder Graduate School.

The authors stress that this work is also important to conservation efforts because leeches are increasingly being collected to survey vertebrate biodiversity. By analyzing their blood meals, researchers are able to identify other animals living alongside the leeches, ranging from wildcats to rats to ground-dwelling birds. 

“If we can identify how leeches find and attach to hosts, we can better understand the results of their gut content analyses,” Fahmy said. “Leeches are also often overlooked and understudied, and, as a natural part of the ecosystem, leeches themselves may be in need of conservation protection.”