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Leafcutter ants make huge piles of waste from cultivating fungus, and these rubbish dumps emit a surprising amount of greenhouse gas.

The ants, found throughout Central and South America, collect huge amounts of vegetation and use it to farm a domesticated fungus in their nests. They have a sophisticated waste management system, with members of the colony responsible for transporting their refuse to a dump outside the colony. This waste consists of decomposed leaves, dead fungus and even dead ants.

Just like compost heaps, these dumps are very rich in carbon and nitrogen, providing ideal conditions for microbes that produce nitrous oxide, a potent greenhouse gas. To work out just how much, Fiona Soper at the University of Montana and colleagues measured the emissions from 22 refuse piles in Costa Rica.

鈥淭hese unique conditions create small areas that have unprecedentedly high emissions,鈥� says Soper, who is now at Cornell University, New York.

Although the dumps are smaller than a dinner table, they can release as much nitrous oxide as human-made systems such as wastewater treatment plants. Soper estimates that in rainforests where these ants live, the refuse piles may generate up to 350 grams of nitrous oxide per hectare per year.

That doesn鈥檛 mean ants are a major contributor to global warming, but it shows they play a major part in the cycling of nutrients in the ecosystem, says Soper. 鈥淲e tend to think of greenhouse gas production being driven by microbes in the soil, and not influenced much by animals,鈥� she says.