Chimps use 'tool kits' to gather army ants

ST. LOUIS, Sept. 9 (UPI) -- U.S. anthropologists say they have discovered chimpanzees in the Republic of the Congo have developed specialized "tool sets" to forage for army ants.

The researchers, led by Washington University in St. Louis Assistant Professor Crickette Sanz in the Republic of Congo's Nouabale-Ndoki National Park, said their discovery provides the first direct evidence of multiple tool use in such a context and suggests the chimpanzees have developed a sustainable method of harvesting food.

"The use of tool sets is rare and has most often been observed in great apes," said Sanz. "Until now there have been no reports of regular use of more than one type of tool to prey upon army ants."

The average number of tools recovered by the team at each site was 3.37, while 36 percent of recovered tool sets contained two types of tools -- nest perforating tools and ant-dipping probes. The scientists said a chimpanzee inserts a probe into a nest or column of ants and gathers the individuals who stream up the tool. The perforating tools are used to open nests so the chimpanzee can gather the ants within.

Chimpanzees that harvest ants by raking a nest open with their hands cause a massive counter-attack from the ants, the researchers said.

The study that included David Morgan of the Lincoln Park Zoo in Chicago appears in the American Journal of Primatology.