21 August 2023

Cotton buds reveal biodiversity in rainforests


Cotton buds, like those used for testing during the COVID-19 pandemic, could become a valuable tool in the accelerating biodiversity crisis. By using cotton buds to wipe leaves, DNA from over fifty animal species can be collected in just a few minutes.

Demonstration of swabbing leaves to sample traces of animal DNA. Photo taken in the Botanical Garden in Greifswald, Germany. Photo: Andreas Sachse.

Carrying 24 cotton buds, three researchers ventured into the dense tropical forest in western Uganda. Elephants, chimpanzees and hornbills occur here. The researchers had a rather unusual purpose: To stroke leaves for three minutes with each cotton bud to collect animal DNA.

These DNA samples now show for the first time that it is possible to collect the DNA of wild animals by simply using a cotton bud. The results have been published in a new study from the Globe Institute at the University of Copenhagen.

“The rainforest is hot and humid and these are conditions that cause DNA to quickly degrade. Therefore, we did not expect great results,” says Postdoc Christina Lynggaard.

But although the researchers were skeptical, they found DNA from over 50 species.

"The 24 cotton buds contained DNA from an incredible variety of animals - mammals, birds and a single frog and a fish. And we found all these animals after a total of just 72 minutes of wiping leaves with cotton buds," says Associate Professor Kristine Bohmann.

Each swab contained, on average, DNA from nearly eight animal species. The species spanned a wide variety of mammals and birds, from very large - as the African elephant weighing just under four metric tons, to the very small - a sunbird weighing just 6.6 grams.

"The study is based on wiping leaves in an ecosystem that is home to a multitude of wild animals and where it has historically been extremely challenging to monitor biodiversity - the tropical rainforest. Here we demonstrate a new method to map the occurrence of animal species,” says Christina Lynggaard.

The 24 cotton buds contained DNA from an incredible variety of animals - mammals, birds and a single frog and a fish. And we found all these animals after a total of just 72 minutes of wiping leaves with cotton buds

Associate Professor Kristine Bohmann. 

This new method can inform on where animal species are found and become a valuable tool in the biodiversity crisis. Animals worldwide are facing grave threats from human activities, with biodiversity loss particularly severe in tropical regions. This loss has far-reaching consequences for the essential services and functions provided by these ecosystems, including pollination and seed dispersal. Monitoring of animal populations is therefore crucial to comprehend the scale of ecosystem changes and to guide the development of effective management strategies. Further, knowing what animals are where is important to assess the risk of spillover of diseases in areas where wildlife can get into contact with humans. 

For it to become an effective tool, it is crucial that the researchers can scale up the methods. And cotton buds are suitable for that.

"Leaf swabbing itself does not require fancy and expensive equipment or lengthy training, and so it can easily be carried out by citizen science programs," says Christina Lynggaard and continues:

"During the COVID-19 pandemic, testing required automated extraction of nucleic acids from millions of swabs per day, and the instruments are now all over the world. What if they could be repurposed to monitor biodiversity on a large scale?"

Cleaning in nature

The new study is part of the research team's work to develop effective DNA-based tools to map the presence of animals.

"We recently showed that it is possible to collect animal DNA directly from the air using a so-called DNA vacuum. The new study is an extension of this work, and we are now working to find out, among other things, whether air filtration provides a more recent snapshot of which animals are present than wiping leaves does, and whether there is a difference in which habitats and ecosystems, which of two methods works best," says Kristine Bohmann and continues:

"I guess you can say that we are specializing in cleaning in nature, how wild animals’ DNA is best collected - with vacuuming or wiping."

The study 'Vertebrate environmental DNA from leaf swabs’ is published in Current Biology. 

About the study

The research is also supported by the VILLUM Foundation with a grant to Christina Lynggaard in their research program 'VILLUM International Postdoc', which supports the advancement of talented postdoc women in their research careers.

The research is further supported by the Carlsberg Foundation with a grant to Kristine Bohmann in their research programme 'Semper Ardens: Accelerate'. This grant has enabled her to establish a research group focused on developing methods to use airborne environmental DNA to monitor birds and mammals.


Postdoc Christina Lynggaard
+ 45 28 99 48 71

Associate Professor Kristine Bohmann
+ 45 40 75 05 21

Journalist and Press Officer Sascha Kael Rasmussen 
+45 93 56 51 68