An Amazonian ant that uses its own "herbicide" to shape its surroundings has been described by scientists. The team made the discovery whilst studying "devil's gardens", mysterious parts of the rainforest that are dominated by a single species of tree. The researchers say the ant injects formic acid into leaves to kill off competing plants, clearing room for its favourite tree to host more nests.
The results of the biologists' study in Peru are reported in Nature magazine.
Rival theories
"They go by the name devil's gardens because the locals think that an evil forest spirit 'Chuyathaqi' lives there," co-author Professor Deborah Gordon, of Stanford University, US, told the BBC News website.
The scientific explanation for their existence, however, has centred on two ideas - with either the Duroia hirsuta tree as the culprit, or the Myrmelachista schumanni ant that lives in their stems.
The trees could "kill off the competition" using chemicals to inhibit the growth of other species around them - a well-known phenomenon scientists call allelopathy.
Alternatively, it may be the ants carrying out the selective destruction.
To investigate, the team planted cedar saplings inside and outside of 10 gardens in the Amazonian rainforest of Loreto, Peru, and either exposed or protected them from the ants.
Saplings free of ants thrived, but those exposed to the ants were promptly attacked.
On show
It was established that worker ants were injecting leaves with a poison called formic acid and the plants started to die within 24 hours.
Formic acid is a toxin common in many ant species; its name actually comes from the Latin for word for ant, formica.
"This is the first case where they are using their formic acid, which ants usually use for interactions with each other such as an alarm signal, on behalf of their host plant," said Professor Gordon.
By killing other plants, the ants provide themselves with many nest sites - a long-lasting benefit as the researchers estimate that the largest garden observed, containing 328 trees over 1,300 square metres, is around 800 years old.
The ants and the devil's gardens are featured in an upcoming BBC documentary series presented by the eminent British naturalist Sir David Attenborough. Called Life in the Undergrowth, the programmes will be screened this November.