The Lives of Ants by Laurent Keller & Élisabeth Gordon

Author:Laurent Keller & Élisabeth Gordon
Language: eng
Format: epub
Publisher: Oxford University Press
Published: 2009-03-20T16:00:00+00:00

Devil’s gardens

Ants take their protective role very seriously and also liberate their tree or shrub from any other plants that might steal its sunlight or hinder its development. This was first observed by an American ecologist, Daniel Janzen, in the 1960s. In Costa Rica he found that the only Cecropia which were not encumbered with climbing lianas were those housing colonies of Azteca ants. When Janzen twined some tresses of a liana about one of the trunks, they were instantly bitten by workers and so did not survive for more than a few days. He tried different experiments in Mexico, depriving certain acacias of their Pseudomyrmex. The immediate result was that the trees started to wither away, whereas those still protected by the ants continued to thrive. Patrolling ants not only attack any Coleoptera such as Colorado beetles, or butterfly caterpillars that trespass on the leaves, they also chew and pull to pieces any foreign plant that happens to grow at the foot of the tree.

In the Amazonian forests the pruning and weeding done by Myrmelachista ants round their trees is even more striking. They regularly climb down from the nest, not to feed but for the sole purpose of destroying any plant that dares to grow within a radius of a few metres from the trunk. They are a dab hand at it too: they attack a young leaf at its most sensitive point, at the base of the vein supplying its nourishment. They begin by biting the leaf; then they turn round and puff a jet of poison from the end of their abdomen into the wound. This substance is a genuine herbicide and will result in necrosis that rapidly spreads along the leaf before affecting the whole unwanted plant, which can thus be eliminated very smartly. Further proof of this was supplied recently by Megan E. Frederickson and Deborah M. Gordon of Stanford University: having planted cedars round the favourite tree of a colony of Myrmelachista schumanni, they saw the ants immediately flock to the intruders and inject their venom into the leaves which, less than twenty-four hours later, had shrivelled. The only cedars to develop normally were some which had been treated with insecticide.

With their good access to sunlight, ant trees will thrive. They soon send up shoots which the ants take over as branches of the main nest, surrounding them with a buffer zone one to three metres in width. This explains why some areas of the Amazonian forest are strangely inhabited by a single species of tree, in clear contrast with the prolific varieties growing in areas close by. People living in these areas called them ‘devil’s gardens’, following the traditional belief that they were the haunt of an evil forest spirit. We now know that the devil lies in the detail of the herbicide used by ants to protect their favourite tree.

Very different sorts of gardens are tilled by Camponotus ants to produce the flowers with which they have an association. In the branches of any sort of tree or shrub they assemble clumps of earth, detritus, and vegetable fibre.

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