Leeches Are Helping Scientists Find Lost Mammals


It looks like a segmented worm, can be found in shallow freshwater, saltwater, in warm, moist soil or clinging to plants or rocks, and it is on the hunt to drink some blood! No, this isn’t a creature from a scary horror movie; it’s a leech. Leeches are related to the common earthworm. They live all across the planet, feeding mostly on freshwater aquatic animals. Leeches are usually known as pests that keep swimmers from diving into some lakes and rivers, but, thanks to new research, they are becoming a biodiversity hero.

forest Southeast Asia
Tropical forests are filled with rare species and, thanks to leeches, scientists are getting the chance to study them.

Leeches to the Rescue

There are around 5,487 known species of mammals in the wild and 25% of them are threatened with extinction. These animals are put at risk by habitat loss, climate change, pollution, and human interference. To help save these species, we first need to understand their population size and where they live.

leeches, university of copenhagen,
Leeches in the lab. Photo Credit: University of Copenhagen

This information can be hard to collect if the animal is good at staying hidden or lives in areas that are hard to get to. That’s where leeches can help! Leeches have a ‘sucker’ at either end of their flattened, muscular bodies. Leeches use these suckers to attach to an animal, called a host. Once attached, the leech will suck the host’s blood, using special chemicals to prevent the blood from clotting (Clotting involves blood forming a solid mass at the place of an injury to stop the flow of blood). Because of all this blood sucking leeches know what animals live in their area, because they are feeding on them, and they have the DNA to prove it!


Discovering DNA

Recently, scientists found that mammal DNA from red blood cells can stay in a leech for up to four months after they have fed on an animal.
sequencing DNA

Researchers wanted to see if this DNA could help them study animals that we don’t know much about, so they set off into the dense forests of Vietnam to collect 25 leeches. Blood samples were taken from the leeches and given to a genetics laboratory. Scientists at the lab sequenced the DNA to identify what animal species the leeches had been feeding on.

The researchers found that the leeches had fed on such animals as the Annamite striped rabbit, small-toothed ferret-badger, Truong Son muntjac, and serow. Until now, these animals were almost impossible to study because they were so difficult to find, but by using blood samples from the leech we can learn how many there are in an area and what type of habitats they live in.

Finding Missing Mammals

15% of the world’s mammals are labeled ‘data deficient’ which means we don’t know enough about them to assess how their population is doing or what their range is. By using the blood samples of leeches we can learn about animals that we’ve never been able to study before, information that we can use to better protect them.

chinese serow grazing forest
Chinese Serow grazing in the forest. Photo Credit: Flickr User, Siwild

If you were a scientist studying animals in the wild what tools would you bring with you into the field? A compass, maybe bug spray? You tell us, post your suggestion in the comments section below.

References: Schnell et al. 2012. Screening mammal biodiversity using DNA from leeches. Current Biology 22:R262-R263.