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Jumping leeches caught on camera for the first time by scientists
After a century of speculation, new footage has confirmed that leeches can jump to get around.
By coiling their body back, the blood-sucking invertebrates are able to throw themselves forward, potentially towards new prey.
Some leeches aren’t just passive parasites but might actively hunt for food.
While the animals generally wait for wildlife to come to them, footage captured in the forests of Madagascar suggests that Chtonobdella leeches aren’t always as patient.
The videos show the leeches bending their body like a spring being pulled back, before throwing its rigid body forward. They don’t appear to have mastered landing though, as they hit the ground in the same pose before starting to move around again.
While the behaviour has only been seen in one leech group so far, anecdotal evidence for other leeches suggest it might be more widespread.
Dr Mai Fahmy, the lead author of the new study, says that their study shows that previously dismissed stories of leeches jumping deserve further investigation.
“There have been previous accounts of leeches jumping, including onto people, but those reports were often explained away as leeches just dropping from branches or attaching to passersby as they brushed against shrubs,” Mai says.
“This study dispels that argument, and we believe it represents the first convincing evidence that leeches can jump and do so with visible energy expenditure.”
The findings of the study were published in the journal Biotropica.
The rings of muscle and lack of a rigid skeleton allow leeches to drink vast amounts of blood, as well as jump. Images © Vital9s / Shutterstock.
How do leeches find food?
Leeches are a large and specialised group of worms which date back more than 266 million years. While some leeches have adapted to eat other animals such as snails, most are sanguinivores, or blood eaters.
To live this lifestyle, leeches have a series of adaptations that help them eat a blood meal. These include sharp teeth or a needle-like proboscis to pierce the skin, a muscular body that can expand as it fills with blood, and a well-developed sensory system.
These characteristics allow leeches to search for prey explains Emma Sherlock, who looks after the Natural History Museum’s leech collections.
“Unlike earthworms, which just have two sets of muscle to support their body, leeches have a third that gives them an extra bit of support,” says Emma. “This allows them to hold their head up and cling to the edge of leaves.”
“They stand there, swaying, and use their senses to detect when animals are coming.”
Until recently, it was thought that leeches tended to ambush their prey, hanging from foliage or overhanging branches to drop or grab onto a passing animal. But for more than 100 years there have been suggestions that some leeches might go further and be able to jump.
The videos taken by the researchers in 2017 and 2023 go some way towards proving this. While they don’t show the leeches jumping onto prey, the footage of them leaping off leaves suggests that it’s something that should be considered.
“Annelids [earthworms, leeches and their relatives] are really muscular animals, so it’s not entirely surprising that they can do this,” Emma adds. “They need these muscles as instead of bone they use muscles and fluid to stay rigid, but we didn’t realise they had that kind of spring in them.”
So far, only the species Chtonobdella fallax has been confirmed as a jumping leech, but the researchers think it’s likely that others do too. By better understanding these behaviours, the scientists hope to find out more about the leeches, as well as the animals they feed on.
“The contents of a leech’s stomach can reveal some of the vertebrates living nearby,” Mai says. “If we can identify how leeches find and attach to hosts, we can better understand the results of their gut content analyses.”
As well as certain leeches, some earthworms are also known to be able to jump. Image © Emma Sherlock.
Can other worms jump?
While the discovery that leeches can jump is a first for these animals, they’re not the first annelids to be recorded leaping into the air. Emma has seen wild earthworms in the Megascolecidae family jumping, but using a different method to the leeches.
“When these earthworms come out of the soil they will jump a few centimetres into the air,” Emma says. “They do this by curling up and putting their head and tail together on the ground, then flicking off it to shoot themselves upwards. It’s quite impressive!”
It’s not entirely certain why they do this, but it’s likely to be a way of avoiding predators.
“Different earthworm species have different ways of getting away from their predators, from leaving their tails behind to squirting a yellow, smelly fluid,” Emma says. “I think the jumping is probably just another technique they use, as it startles the predator as well as giving the worm a headstart to get away.”
It’s not just earthworms either. A variety of other worm-like invertebrates can jump, from the legless larvae of gall midges to Calindoea trifascialis caterpillars. Skipper flies, meanwhile, get their name from the behaviour of their maggots, which tense their bodies and release them to propel themselves forward.
With video recording now an increasingly common part of daily life, more invertebrates could be captured jumping on camera in the coming years and reveal their more athletic side.
