A recent study presented video evidence that at least one species of terrestrial leech can jump, a behavior that scientists have debated for over a century. Researchers from the American Museum of Natural History, Fordham University, and City University of New York published the footage and analysis in the journal Biotropica. Lead author Mai Fahmy stated that this is the first convincing evidence of leeches jumping with visible energy expenditure, dispelling previous accounts of leeches attaching to people as they brushed against shrubs or dropped from branches.
During expeditions to Madagascar in 2017 and 2023, Fahmy recorded footage of leeches from the genus Chtonobdella coiling back on a leaf and then taking off. The motion was compared to a backbending cobra or a spring being pulled back as the leeches kept their bodies extended while soaring through the air. This behavior was a departure from their usual inchworm-like movements, leading to a hard landing. Similar jumping behaviors are observed in other worm-like invertebrates such as gall midge larvae and skipper flies, but the ability of terrestrial leeches in the family Haemadipsidae to jump has been a topic of debate among naturalists and leech biologists.
The jumping leech observed on the 2023 trip was identified as Chtonobdella fallax, a common species in Madagascar. The larger Chtonobdella group of leeches, to which C. fallax belongs, can be found across Madagascar, the Seychelles, the Malay Archipelago, and the South Pacific Islands. The researchers do not know how often this behavior occurs or if leeches use it to seek out hosts, but they caught multiple jumps in two short recordings, suggesting that jumping may be common for this species. Understanding overall leech behavior is crucial for conservation efforts, as leeches and their blood meals are used to survey vertebrate biodiversity.
The study authors believe that identifying how leeches find and attach to hosts can help researchers understand the results of gut content analyses. Leeches, often overlooked and understudied, are a natural part of the ecosystem and may need conservation protection. With leeches being increasingly collected for biodiversity surveys, knowing their behavior can help in conservation efforts. Michael Tessler, the coauthor of the study, highlighted the importance of understanding leech behavior for conservation purposes and stated that leeches play a vital role in the ecosystem that may need protective measures.