Spiderwebs are beating every other method at counting wildlife — and fake webs work too

The unglamorous spiderweb just became one of conservation biology’s most effective instruments. Researchers have discovered that the sticky silk traps environmental DNA — or eDNA — shed by passing animals, from saliva to pollen to skin cells, creating a passive census tool that outperforms nearly everything else scientists have tried.

Joshua Newton, a molecular ecologist at Curtin University in Perth, put webs head-to-head against vegetation swabs, water samples, soil, and a filter-equipped fan near a zoo and wildlife sanctuary. Vegetation picked up more forest mammals. Water caught more fish. But webs identified the broadest range of vertebrates overall — a result that echoes a similar study from France. Newton’s verdict on the material: “It’s probably one of the best substrates we’ve used and tried to date.”

The catch is real, though. Collecting meaningful data meant destroying roughly 40 spiderwebs. “It kind of goes against everything that we’re trying to do if we’re collecting the home of an organism,” Newton admits. That tension caught the attention of Angela McGaughran, a genomicist at New Zealand’s University of Waikato. Her workaround is almost comically simple: she bought fake cobwebs from a Halloween store, stretched them over coat hangers, and hung them outside. The synthetic webs snagged eDNA from nearby cows, sheep, and birds at a local aviary — and detected fungal spores even better than the real thing.

That fungal result could matter beyond the novelty. Plant pathologists monitoring agricultural threats now have a reason to pay attention, and McGaughran’s team is scaling up experiments to see whether cheap artificial webs can be deployed as DNA traps anywhere. The idea that a $2 Halloween decoration might eventually replace expensive field equipment or labor-intensive surveys is exactly the kind of low-tech pivot that makes ecology interesting. Whether the approach holds up across climates, seasons, and species densities remains an open question — but the early evidence suggests spiders have been running better biodiversity surveys than we have all along.