When a lion decides to chase down a zebra it seems as though nothing can stop it. But now researchers have discovered these enormous predators are being thwarted by a tiny foe: ants.

Scientists have found the spread of big-headed ants in east Africa sets off a situation leading to lions making fewer zebra kills.

Prof Todd Palmer of the University of Florida, a co-author of the research, said the findings were a surprise. “I was stunned,” he said. The fewer kills appear to be due to the upending of a crucial relationship – between native ants and the trees in which they live, causing a loss of cover for lions.

Palmer said the discovery highlighted the importance of interactions between species. “We often talk about conservation in the context of species,” he said. “But it’s the interactions which are the glue that holds the entire system together.”