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

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

Mushroom-farming ants forage for vegetation to feed cultivated mushrooms grown inside their colonies. In turn, the fungi act 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 incorporating a carbonate biomineral into their armor. The ants do this through a symbiotic relationship with Pseudonocardia bacteria, which transform CO2 into rock using chemical processes that are not yet well understood.

Now the team has discovered that another mushroom-farming ant, Sericomyrmex amabilisfound in Central and South America, can do the same without symbiotic bacteria, becoming the first known animal to have developed this ability.

Remarkably, the mineral they make is dolomite, which is extremely difficult for chemists to produce in the laboratory. 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 of Zhejiang University in China.

Dolomite consists of calcium, magnesium and carbonate. Forming dolomite in the lab is difficult because magnesium clings to surrounding water molecules and does not fit easily into the calcium carbonate structure, which slows crystal formation, says Currie. To try to overcome this, he says, researchers use high temperatures and pressures. The next phase of the team’s research will seek to understand how ants are able to achieve this feat.

For mushroom-farming ants, turning CO2 into stone solves at least two problems: strengthening the ant’s exoskeleton 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,” says Currie.

In an effort to counteract global warming, scientists are exploring techniques to convert atmospheric CO2 into carbonate minerals, essentially turning carbon into rock. “These ants are the first animal shown to engage in such a process, and offer exciting potential as a model for human intervention,” says Currie.

Cody Freas of the University of Toulouse, France, who was not 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 sinks, converting atmospheric carbon dioxide into a protective mineral armor,” says Freas. “This dual solution helps the ants both regulate the nest atmosphere and create a bioengineered physical defense.”