Imma Perfetto
Cosmos science journalist
Settling a debate which has persisted for more than a century, researchers have shown that at least one species of terrestrial leech can indeed jump.
A new paper in the journal Biotropica presents the first video evidence of the feat.
“We believe this is the first convincing evidence that leeches can jump and do so with visible energy expenditure,” says lead author Mai Fahmy, of the American Museum of Natural History and Fordham University in the US.
“There have been previous accounts of leeches jumping, including onto people, but those reports were often explained away as leeches just attaching to a passerby as they brushed against shrubs or dropping from a branch above. This study dispels that argument.”
During expeditions to Madagascar in 2017 and 2023, Fahmy recorded footage of 2 different leeches intentionally jumping off leaves and onto the ground.
This video taken in Madagascar in 2017 shows a Chtonobdella leech taking a small jump followed by a big leap to the ground. Credit: © Mai Fahmy
In what Fahmy and co-author Michael Tessler, of the American Museum of Natural History and the City University of New York, liken to a “back bending cobra or a spring being pulled back to maximise potential energy” the leech begins by coiling its body back.
It then propels itself into the air, keeping its body extended as it soars towards the ground. This is a departure from its usual locomotion, which is a looping motion similar to that of an inchworm.
“Essentially, it executes a graceful jump but with a seemingly hard landing,” says Tessler.
Fahmy collected the leech she observed in 2023 and identified it as Chtonobdella fallax, a common species found in Madagascar. Chtonobdella leeches are part of the family Haemadipsidae, for which the debate about jumping ability has endured through anecdotal evidence since the late 19th century.
This video taken in 2023 in Madagascar shows two Chtonobdella leeches questing on the same leaf and briefly interacting with each other. Then, as in the 2017 video, one leech assumes a recoiled body posture before jumping from the leaf to the ground. Credit: © Mai Fahmy
The researchers say their observations establish that at least 2 terrestrial leeches possess the musculature, coordination, and inclination to execute a jump.
“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 2 short recordings, this behaviour may be common for this species,” says Fahmy.
Understanding leech behaviour is valuable as they are increasingly being collected to survey vertebrate biodiversity via the blood they feed on.
“If we can identify how leeches find and attach to hosts, we can better understand the results of their gut content analyses,” says Fahmy.
“Leeches are also often overlooked and understudied, and, as a natural part of the ecosystem, leeches themselves may be in need of conservation protection.”
