White men can’t jump, but earthly leeches can. This is now a scientific fact; after centuries of anecdotal reports, the parasites have been captured on video jumping from leaves in Madagascar’s rainforest.
The images were first captured in 2017 by Mai Fahmy, a researcher now at the American Museum of Natural History. She had a chance encounter with a leech that extended its body in search of a host, a behavior known as ‘scavenging’. The adventurous leech was found in Madagascar’s Ranomafana National Park.
Fahmy pulled out her phone and caught the leech coming forward and then jumping off the leaf and landing with a flail or two on the forest floor. The footage – as well as a 2023 video showing the acrobatics – was published today Biotropics.
“Even though I was in Madagascar collecting leeches for blood meal analysis, the pressure was on to see if we could get another video to support the claim we’re making in the paper,” Fahmy said. With the publication of the study, the team confirms anecdotal evidence that the terrestrial parasites (at least the species Chtonobdella fallax) jump in search of a warm, blood-filled morsel to feed on.
Jumping leeches even appeared in the chronicles of the famous 14th century explorer Ibn Battuta, who documented the behavior in leeches in Sri Lanka, indicating that the behavior may have evolved independently in different land leeches. But by the mid-20th century, the idea of jumping leeches was viewed more skeptically in scientific publications.
“A lot of the history of this really comes down to the question, ‘What exactly is a jump?’ For hundreds of years, there were anecdotes from very well-trained observers about jumping leeches,” said Michael Tessler, an invertebrate zoologist at the American Museum of Natural History and Medger Evers College, in a phone conversation with Gizmodo. “It wasn’t until people started studying leeches more seriously, sometime in the 19th century, early 20th century, that almost every leech biologist who spent time with these things said, ‘There’s no way they can jump.’‘”
It was no secret that leeches sometimes fall on their hosts, but the question on the table was about intentionality: do the leeches expend energy in launching toward a target (or simply into the air), or do they fall over, causing gravity to can do work? them? The video evidence now documents that the parasites do the former, coiling up and then lunging forward into the unknown. The animals are certainly moving outwards from their green launching pad, and – the team argues – perhaps slightly upwards. In other words, they jump.
Tessler said the leeches are likely jumping as they search for a host. After seeking out movement or warmth from a potential meal, the animals may leap towards the host in a sort of leap of faith.
Fahmy has been bitten by leeches before, including at least one time when one of the parasites landed in her eye. The leeches like to go for the eyes, she said. Once captured, the animals’ blood meals can be sampled to gain insight into the rainforest’s wildlife. The leech is actually a mobile environmental DNA laboratory.
“I will be going back to Madagascar in the next few years,” Fahmy said. “I’ll keep my eyes on the leeches. We know so little about their biology, their natural history, their behavior. They are full of mystery.”
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