Acacia trees' ingenious secret

A tree that employs guards in the form of aggressive soldier ants has revealed a remarkable new secret to British scientists. The relationship between ants and the Acacia tree in eastern Africa is one of nature's best known examples of co-evolution.

In return for food and shelter on the trees, the ants ward off hungry herbivores and perhaps even encroaching vegetation. But scientists have always been mystified by how bees and other "friendly" insect pollinators are able to get through the formidable ant defences.

Now researchers led by Pat Willmer from St Andrew's University, Scotland and Graham Stone from Oxford University have discovered that young Acacia flowers appear to produce a volatile chemical signal at a crucial stage in their development that keep the ants away, allowing pollinating insects to visit unmolested during this time.

The ants patrol young buds, and return to the flowers at a later stage to protect the developing seeds.