Using leeches to index rare mammals

You’ve heard of using leeches for bloodletting, a practice that is making a comeback for a few specific conditions. Well, that’s not all leeches are good for. Ida Bærholm Schnell and Philip Thomsen and their colleagues from the University of Copenhagen and the University of Cambridge have been using the little parasites to catalogue endangered species.

It’s exceedingly difficult to monitor rare mammals in remote regions because, well, the animals are rare and the regions are remote. Unlike humans, leeches seem to have no trouble finding mammals. Thanks to modern sequencing techniques, mammalian DNA can be extracted from leeches after their last blood meal. What makes leeches particularly useful is that fact that they store this meal for many months.

After successfully testing the extraction of goat DNA from leeches killed four months after their last meal, the scientists left the lab and set out to collect leeches from the dense forests of the Central Annamite region of Vietnam. Almost all the captured leeches (21 our of 25) contained mammalian DNA. Six different mammals had donated their blood to the leeches, two of which had only recently been described and two others of which were considered ‘threatened’.

As Mads Bertelsen from the Coopenhagen Zoo explains:

Leeches come to you with the blood samples, rather than you tracking down the animals in the jungle. Simple and cheap, and the sampling does not require specially trained scientists, but can be carried out by local people. I am convinced that this technique will revolutionize the monitoring of threatened wildlife in rainforest habitats.