When West African chimps go dipping for ants -- using long, slender tools to scoop the insects out of the ground instead of digging with their hands -- their tool of choice is a shrub called Alchornea hirtella. According to a study published Wednesday in the American Journal of Primatology, chimps show a surprising preference for this one species of plant. If it isn't readily available, they'll search for it extensively before they give up and use something else.
The shoots of this plant make excellent dipsticks. In fact, they serve two purposes: Thicker shoots are used to dig up ant nests and anger the insects inside. When a thinner shoot is dipped into the disturbed nest, the livid ants swarm up the tool. Chimps use their fingers to swipe the ants off into their other hand, then eat them all at once.
This process allows them to eat large quantities of ants -- which the study, based on more than a decade of observational data, suggests are a bigger part of their diet than scientists previously thought -- without getting bitten by hoards of angry insects.
Chimps are known tool users, so it's not surprising that they've developed such a tidy technique. But the specificity of the tool is intriguing. Lead author Kathelijne Koops, a postdoctoral researcher at the University of Cambridge, said in a statement that the observed chimps would only fashion tools out of other plants after exhaustive searches for Alchornea hirtella.
But how did this shrub take West African chimps by storm?
"Scientists have been working on ruling out simple environmental and genetic explanations for group differences in behaviors, such as tool use, and the evidence is pointing strongly towards it being cultural," Koops said in the statement. "They probably learn tool use behaviors from their mother and others in the group when they are young."
And they can adapt those tools for other purposes, too. In the video above, a chimpanzee has discovered one of Koops's cameras. He uses a tool to poke and prod at the foreign device, then sniffs the poking end of the tool to get some info.