Leeches suck. Most people try to avoid them. But in the summer of 2016, park rangers in China’s Ailaoshan Nature Reserve went on the hunt for the little blood wolverines.
For months, rangers searched the reserve’s evergreen forest, collecting tens of thousands of leeches by hand and sometimes ripping the slimy parasites from the rangers’ own skin. Whenever the rangers found a leech, they placed it in a small tube filled with preservative, stuffed the tube into a fanny pack, and moved on. The work could help conservation efforts, at Ailaoshan and elsewhere.
There are many ways to measure how much effort goes into conserving wildlife, but it’s hard to assess the success of that effort, even in protected areas, says Douglas Yu, an ecologist at the Kunming Institute of Zoology in China.
But bloodthirsty maggots may just be the right tool for the job. Leeches aren’t picky eaters: they feast on the blood of many different creatures, from amphibians to mammals to fish. Scientists have shown that they can extract animal DNA from blood that leeches and other bloodsucking creatures have ingested, known as invertebrate-derived DNA, or iDNA, and identify the animal of origin.
And some researchers suggested that iDNA, a type of environmental DNAcould be used to track the ranges of animals in an area, says Yu (Serial number: 01/18/22). “We thought we would just try to do it.”
Recruiting 163 park rangers, Yu and his colleagues tasked leech hunters to collect the parasites along the rangers’ regular patrol routes, which covered all 172 areas of the reserve.
Three months later, the rangers had collected 30,468 leeches. After extracting and analyzing animal DNA from the leeches’ blood meals, Yu and his colleagues detected the presence of 86 different species, including Asian black bears, domestic cattle, endangered Yunnan spiny frogs, and, of course, humans.
And what is more, iDNA gave clues to where animals preferred to roamresearchers report March 23 in nature communications. The researchers found that wildlife biodiversity was greatest in the high-altitude interior of the reserve, while domestic cattle, sheep and goats were more abundant in the lower, more accessible areas of the reserve. Because most detected wildlife species should be able to inhabit all parts of the reserve, the dichotomy suggests that human activity may be driving wildlife out of certain areas, Yu says.
Compared to other methods of studying wildlife, using iDNA from leeches is “really cost-effective and time-efficient and doesn’t require a lot of experience,” says Arthur Kocher, an ecologist at the Max Planck Institute for the Science of Human History in Jena, Germany. , who did not participate in the study.
Camera traps, for example, are triggered only by animals of a sufficiently large size, and the instruments are expensive. Sight-based surveys require trained observers. With leeches, Kocher says, “there are clear advantages.”
Yu and Kocher suspect that leeches and other blood-sucking creatures, such as carrion flies or mosquitoes, will become more popular wildlife surveillance tools in the future. People are becoming more aware of what iDNA brings to the table, says Yu.