Moissl-Eichinger and her colleagues have shown that the standard sequencing method often detects no archaeal species, or just one, in samples taken from people’s bodies. But when her team used a version of the sequencing method optimised to detect archaea in the same samples, it revealed that there were in fact dozens of these species present.

Each part of the body seems to be home to characteristic species of archaea, as with bacteria.

What’s more, in the nose and appendix, individual archaea cells outnumbered those of bacteria. “We did not expect that,” says Moissl-Eichinger. Because we have only just discovered them, we don’t know what most of the archaea in our bodies do.”