Ants capture carbon dioxide from the air and turn it into armour

An ant that can turn carbon dioxide in the air into dolomite stone in its exoskeleton may hold clues to how humans can sequester greenhouse gases to avert climate disaster.

Fungus-farming ants forage for vegetation to feed cultivated fungi that are grown inside their colonies. In turn, the fungi serve as the primary food source for the ants. The high density of ants and fungi can result in high concentrations of CO2 inside the nests.

In 2020, Cameron Currie at the University of Wisconsin-Madison and his colleagues found that the ants of the species Acromyrmex echinatior incorporate a carbonate biomineral into their armour. The ants do this through a symbiotic relationship with Pseudonocardia bacteria, which transform CO2 into rock using chemical processes that aren’t yet properly understood.

Now the team has discovered that another fungus-farming ant, Sericomyrmex amabilis, which is found in Central and South America, can do the same thing without symbiotic bacteria, becoming the first known animal to have evolved this ability.

Remarkably, the mineral they make is dolomite, which is extremely difficult for chemists to produce in the lab. Dolomite rocks, such as those found in Italy’s Dolomite mountains, require millions of years and complex geological processes for the calcium and magnesium atoms to align perfectly. Yet the ants do this quickly and effortlessly, without high temperatures, says team member Hongjie Li at Zhejiang University in China.

Dolomite consists of calcium, magnesium and carbonate. Forming dolomite in the lab is difficult because magnesium holds tightly onto surrounding water molecules and doesn’t easily fit into the calcium carbonate structure, which slows down crystal formation, says Currie. To try to overcome this, he says, scientists use high temperatures and pressures. The next phase of the team’s research will attempt to understand how ants are able to accomplish this feat.

For fungus-farming ants, turning CO2 into stone solves at least two problems: strengthening the ants’ exoskeletons and preventing the build-up of toxic CO2 inside the colony.

“We have discovered a natural system that has evolved, over millions of years, to reduce the toxic accumulation of atmospheric CO2 in an ant colony,” Currie says.

In an effort to counteract global warming, scientists are exploring techniques for converting atmospheric CO2 into carbonate minerals, essentially turning carbon into stone. “These ants are the first animal shown to be engaging in such a process, offering exciting potential as a model for human efforts,” says Currie.

Cody Freas at the University of Toulouse, France, who wasn’t part of the study, describes the ants’ ability to turn CO2 into dolomite as a “remarkable adaptation”. “Individuals take on the role of living carbon scrubbers, converting atmospheric carbon dioxide into a protective mineral armour,” says Freas. “This dual solution both helps the ants regulate their nest atmosphere and create a bioengineered physical defence.”