ANTS were accomplished farmers long before humans acquired the knack, and now it seems their agricultural prowess even extends to the use of herbicides.
Previous studies have shown that leafcutter ants make compost in their nests to grow an edible fungus, while other types of ants keep “herds” of aphids in order to harvest their secretions of nutritious plant juices.
But Megan Frederickson and her colleagues at Stanford University in California wanted to know whether the ant Myrmelachista schumanni could be responsible for cultivating large clumps of trees in the Amazonian rainforest that are made up almost entirely of one species, Duroia hirsuta, in which the ant lives.
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To see whether these devil’s gardens, as they are known locally, are the ant’s handiwork or the result of competition between tree species, Frederickson planted saplings of a common Amazonian cedar either inside or outside the gardens, protecting just some of the saplings from the ants.
Within five days, worker ants had devastated the unprotected saplings in the garden by poisoning them with formic acid, causing most of the leaves to drop off (Nature, vol 437, p 495).
This behaviour could allow more D. hirsuta trees to grow in the area cleared by the ants, enabling the colony to massively expand its number of nest sites, says Frederickson. This may explain how some colonies live as long as 800 years.
