But these errant strands of DNA do not just settle into muddy soil or flow along rivers. The air itself is infused with genetic material. A simple air filter running for hours, days or weeks can pick up signs of nearly every species that grows or wanders nearby.

As a proof of concept, the researchers showed that they could pick up signs of hundreds of different human pathogens from the Dublin air, including viruses and bacteria. Such surveillance could help scientists track emerging diseases. The same method can track common allergens, like peanut or pollen, more precisely than is currently possible, the scientists discovered.