The team studied the pattern of scratches on the tools using sophisticated microscopic techniques and image analysis software.
South African and French researchers have demonstrated how the human-like species known as Australopithecus robustus used long, sharp bones to forage for insects. It is said to be the oldest, direct evidence for a particular food resource in hominids.
The new findings may solve the puzzle of why remains of the ape-man contain significant amounts of a type of carbon associated with eating protein. They also support the idea that the creature was far more sophisticated than science has so far acknowledged.
"All the school textbooks tell you that this robust ape-man was not really a tool user - that he was just a zombie who went extinct," Lucinda Backwell, from Witwatersrand University in Johannesburg, told BBC News Online. "This is not the case."
Researchers dig in
A. robustus is not a direct ancestor of modern man but a distant cousin, arising from a different branch of the human family tree.
Fossilised implements excavated with A. robustus remains, and thought to represent the world's oldest-known bone tools, were subjected to a reanalysis by Backwell and Francesco d'Errico, of the Centre National de la Recherche Scientifique in Talence, France.
The team studied the pattern of scratches on the tools using sophisticated microscopic techniques and image analysis software.
They found that the wear patterns were unlike those produced on tools used for digging up tubers, but closely matched those produced on experimentally created bone tools used by the researchers themselves to open up termite mounds.
The fact that the ancient tools are all of a particular shape and size - they range from 13 to 19 centimetres in length - demands a reappraisal of the mental abilities of A. robustus, the team believe.
Backwell said: "It is showing us that these robust ape-men had the cognitive ability to select for a particular type of bone. It wasn't opportunistic."
Rich food source
The study also helps explain the relatively high levels of a type of carbon, known as C4, which are found in A. robustus skeletons. This type of carbon is laid down in the bones of meat eaters. This would fit with the consumption of termites, which are rich in both proteins and fats. "It all gels," said Backwell.
"It accounts for the meat, but it's not meat as we would normally perceive it - it's insects."
The research team report their work in the Proceedings of the National Academy of Sciences, a major international journal. In their paper, they write: "Chimpanzees are known to 'fish' for termites by using grass stalks to perforate and dig termite mounds in a variety of ways, but never with bone implements.
"By digging termites out of their nests, hominids would have made use of a rich food source that was otherwise accessible only after rain when the insects emerge from their nests for breeding."
Study the similarities between image (A) and image (D). The markings are almost identical. (A) is a fossil tool more than one million years old, (B&C) are experimental tools used to dig up tubers and bulbs; (D) is an experimental termite tool.