Spiderwebs Turn Out to Be a Rich Source of Environmental DNA for Wildlife Surveys

Counting the creatures in an ecosystem is central to conservation work — it helps scientists gauge biodiversity, track migration and spot invasive species — but traditional census methods that rely on humans seeing, trapping or sensing animals can be slow, costly and full of gaps. Over the past decade, researchers have turned to environmental DNA, or eDNA: genetic material that living things shed into scat, soil, water and air, which can be collected and sequenced without ever spotting the animal itself.

Researchers have now identified an unexpected eDNA source: spiderwebs. The sticky strands trap material from the spiders that spin them, crumbs from their meals, and saliva and pollen from nearby plants and animals. "It's probably one of the best substrates we've used and tried to date," said Joshua Newton, a molecular ecologist at Curtin University in Perth, Australia, who has also sampled flowers, streams, tree hollows and even filters on moving cars to study animal populations.

Newton compared the biological diversity captured in spiderwebs with that from vegetation swabs, water, soil and a filter-equipped fan near a zoo and wildlife sanctuary outside Perth. Vegetation swabs revealed more forest mammals and water samples identified more fish, but no other passive tool matched spiderwebs' ability to identify vertebrate species — a result that echoed a similar study conducted in France. Gathering the data required destroying about 40 webs, which Newton said "goes against everything that we're trying to do if we're collecting the home of an organism."

That concern led Angela McGaughran, a genomicist at New Zealand's University of Waikato, to try an alternative: she bought a bag of fake webs from a Halloween store, wrapped them around coat hangers and hung them outside. The synthetic webs snagged eDNA from nearby cows, sheep and exotic birds at a nearby aviary, and detected fungal spores better than real webs did — useful for plant pathologists watching for agricultural threats. Her group is now running larger experiments to see whether artificial webs can offer a cheap, efficient way to collect eDNA anywhere.