Welcome to the spiderverse, a world measured through webs

Counting the creatures in the world around us is critical for a raft of conservation efforts. It helps scientists gauge biodiversity, track migration, and spot invasive species. That census-taking, though, often requires humans to tabulate what they see, trap, or otherwise sense—a potentially laborious, costly process that can still leave gaps. But developments over the last decade have revolutionized eco-surveillance. Biologists have tapped into sequencing technology to analyze environmental DNA, or eDNA—genetic material shed by living things. Samples collected from scat, soil, water, and air have opened up a new avenue scientists can use to monitor endangered species and detect invasive ones before anyone can even lay eyes on them. More recently, they’ve uncovered an eDNA gold mine: spiderwebs. The naturally sticky stuff traps material from its arachnid creators, crumbs from their suppers, and, crucially, bio-detritus like saliva and pollen from nearby plants and animals. Every living thing, it seems, sheds copious DNA all over the place, including into the air, and webs then easily ensnare it. “It’s probably one of the best substrates we’ve used and tried to date,” says Joshua Newton, a molecular ecologist at Curtin University in Perth, Australia, who’s sampled flowers, streams, hollows of dead trees, and even filters on moving cars to study vertebrate populations. Newton recently compared the biological diversity in spider­webs with that found in other sources—including vegetation swabs, water, soil, and a fan outfitted with a filter—near a zoo and wildlife sanctuary outside Perth. Each had its obvious strengths: The vegetation swabs revealed more forest mammals, and the water samples identified more fish. But no passive tool matched spiderwebs’ ability to ID vertebrates, echoing results from a similar study conducted in France. Here’s where things get sticky: To gather meaningful data, they had to destroy about 40 webs. “It kind of goes against everything that