The ant in the devil’s garden

Within the extraordinary biodiversity of the Amazon rainforest lie circles of a single tree species – the devil’s gardens. And these pockets of uniformity are created by ants.

Ants in the devil's garden
Vojtěch Zavadil, CC BY-SA 3.0, via Wikimedia Commons

If you take a stroll through the Amazon rainforest, you’ll see a huge variety of trees and plants. There are around 16,000 different tree species in the rainforest, at last estimate, and around 438,000 different plant species. These trees and plants are locked in a perpetual and ruthless battle for territory. Who can capture the sunlight? Who can spread their species the furthest? And some of these trees and plants recruit an unlikely ally in this battle: ants.

The ants and the trees have a treaty. The first party: trees or shrubs such as Duroia hirsuta or Cordia nodosa. The second party: Myrmelachista schumanni, commonly known as lemon ants (because they smell like lemons). The lemon ants turn these trees into a thriving ant metropolis. They live in the plant’s hollow stems and eat their leaves.

In exchange for this comfortable home, the ants act as the plant’s standing army. Whenever another species takes root nearby, the ants mobilise. They inject the competing plant with formic acid, poisoning it. The lemon ants will even fight off other ant species that want to feed on their host plant. Within the territory shared by this ant and this tree, no competitors can thrive.

The result is uncanny. Imagine a circular hole in the rainforest. An eerie clearing completely lacking in botanical biodiversity, with just a single species (or sometimes two or three equally friendly to the ants). These are the devil’s gardens.

Devil’s gardens can be found in many different sections of the Amazon rainforest. They can get surprisingly large – researchers have found one supporting six hundred trees. They can also last a surprisingly long time – up to eight hundred years in one case. The biological term for this relationship is mutualism: both the plant and the animal benefit from this evolutionary treaty.

[I promised to write about this back in the post on vegetarian spiders.]

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