F. Soper et al., Proceedings of the Royal Society B, 10.1098 (2019)

Leafcutter ant ‘compost piles’ produce potent greenhouse gases

Leafcutter ants are known for producing lots of trash. In fact, the species Atta colombica (above) can create bathtub-size, thigh-high mounds of refuse that contain not only leaves, but also ant poop, bacteria, and dead ants. Now, researchers have discovered these massive compost piles are potent sources of greenhouse gases.

Researchers analyzed the exhalations of 22 leafcutter mounds in southwestern Costa Rica. They found that in the humid, oxygen-poor conditions of the piles, bacteria produce prodigious amounts of methane and nitrous oxide. Levels of methane seeping from the mounds were about 20 times higher than those emanating from the surrounding forest floor. But the big surprise was nitrous oxide, which left the mounds in concentrations 1000 times or more above background levels, the researchers report online today in the Proceedings of the Royal Society B.

Such rates rival or exceed those from wastewater treatment plants and dairy manure lagoons. But how they affect the climate is unknown—that’s because coming up with an estimate of total emissions, from A. colombica and the nearly four dozen other species of leafcutter ants, might be next to impossible. However, their research may have explained one mystery: why other studies have detected widely varying levels of methane and nitrous oxide in the regions where some of these ants live.