London: Chimpanzees search for the right tools from a key plant species when preparing to 'ant dip' - a technique that enables them to feast on army ants without getting bitten, a new study has found.
West African chimpanzees will search far and wide to find Alchornea hirtella, a spindly shrub whose straight shoots provide the ideal tools to hunt aggressive army ants, researchers said.
The plant provides the animals with two different types of tool, a thicker shoot for 'digging' and a more slender tool for 'dipping'.
On locating an army ant colony, chimpanzees will dig into the nest with the first tool - aggravating the insects. They then dip the second tool into the nest, causing the angry ants to swarm up it.
Once the slender shoot is covered in ants, the chimpanzees pull it out and wipe their fingers along it: scooping up the ants until they have a substantial handful that goes straight into the mouth.
This technique - 'ant dipping' - was previously believed to be a last resort for the hungry apes, only exploited when the animal's preferred food of fruit couldn't be found.
But the latest study based on over ten years of data, showed that, in fact, army ants are a staple in the chimpanzee diet - eaten all year round regardless of available sources of fruit.
Ants may be an important source of essential nutrients not available in the typical diet, said researchers, as well as a potential source of protein and fats.
"Ant dipping is a remarkable feat of problem-solving on the part of chimpanzees," said Dr Kathelijne Koops from the University of Cambridge's Division of Biological Anthropology and Junior Research Fellow of Homerton College.
"If they tried to gather ants from the ground with their hands, they would end up horribly bitten with very little to show for it.
"But by using a tool set, preying on these social insects may prove as nutritionally lucrative as hunting a small mammal - a solid chunk of protein," Koops said.
Koops pointed out that if Alchornea hirtella is nowhere to be found, chimps will fashion tools from other plants - but seemingly only after an exhaustive search for their preferred tool provider.
Koops also addresses another question - how do chimpanzees acquire knowledge of such sophisticated techniques?
"Scientists have been working on ruling out simple environmental and genetic explanations for group differences in behaviours, such as tool use, and the evidence is pointing strongly towards it being cultural," said Koops.
"They probably learn tool use behaviours from their mother and others in the group when they are young," Koops said.
The new research was published in the American Journal of Primatology.