Jumping leeches

Video: How Chtonobdella leeches jump off leaves. © Mai Fahmy, American Museum of Natural History

You might think that the worm-like parasites can only crawl. But some leeches can apparently even move by hopping. This suspicion has now been confirmed for the first time by video recordings of a representative of the land-dwelling leeches. The forest dweller of Madagascar builds up tension by bending and then catapults itself through the air. It is possible that the bloodsuckers use this technique not only to move, but also to jump on their victims.

Here, they only lurk in ponds and lakes, waiting for an opportunity to bleed: the blood-sucking leech species of Europe are freshwater dwellers and move around swimming and on the bottom of the water. But in addition to these aquatic representatives of the parasites, there are also so-called land leeches (Haemadipsidae) in some parts of the world. These notorious pests are in the forests of South Asia, Australia and on some islands in the Indian Ocean, looking for victims – which include various vertebrates and humans. The worm-like creatures move along the ground and through the vegetation in a similar way to geomancy caterpillars.

Exaggerated reports?

But terrestrial leeches have long been said to have another ability: they are supposedly able to pounce on their victims. However, this jumping behavior has not been scientifically proven so far and has been doubted by some experts. “Reports of leeches jumping on people have often been explained by saying that they were just clinging to passers-by or falling from a branch. Our study now refutes these arguments,” says lead author Mai Fahm from the American Museum of Natural History in New York.

Together with her colleague Michael Tessler, the researcher now presents video evidence that at least one species of land leech can actually jump. The recordings come from two separate expeditions in the forests of the island of Madagascar. They show the locomotion behavior of a species from the Chtonobdella leech group, which, in addition to Madagascar, also occur in the Seychelles, the Malay Archipelago and the islands in the South Pacific.

Jumping behavior documented

The videos initially show Chtonobdella fallax specimens in their typical caterpillar-like locomotion. Then, however, you can see the leeches bend slightly before jumping off a leaf. “With each jump, the leech rolls back before taking off. Visually, it looks a bit like a cobra bending backwards, or a spring being pulled back to accumulate energy,” write Fahm and Tessler. After jumping, the leech then keeps its body stretched out as it whizzes through the air. “To our knowledge, this is the first convincing evidence that leeches can jump and do so with visible expenditure of energy,” says Fahmy.

Screenshots of the individual steps of the jumping behavior of Chtonobdella fallax. © Mai Fahmy

The bloodsuckers now join a small group of other worm-like creatures that are known to have jumping abilities: These include the larvae of gall midges and some caterpillars of butterfly species. They are also known to assume a hunched posture before catapulting themselves into the air. “We don’t know how often Chtonobdella fallax displays this jumping behavior or to what extent the leeches also use this ability to search for hosts. But since we documented several jumps in two short recordings, the behavior could at least be typical for this species,” says Tessler.

Finally, the researchers point out that a better understanding of the biology of leeches can even benefit conservation, as the parasites are sometimes collected to study the biodiversity of vertebrates in certain regions based on their blood meals. “If we can find out how leeches find and attach themselves to their hosts, we can better understand the results of analyses of their gut contents,” says Fahmy. She also advocates a more positive view of these often disdained creatures: “As a natural part of the ecosystem, leeches may themselves need to be protected,” says the scientist.

Source: American Museum of Natural History, scientific article: Biotropica, doi: 10.1111/btp.13340

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