It all starts with the whistling-thorn acacia trees in the plains of Laikipia, Kenya. These thorny trees had developed a mutually beneficial relationship with the local acacia ant: The trees provide shelter and food for the ants and in return they use their stinging bite to discourage hungry elephants from devouring the trees.

But the big-headed ant changed all that.

Thought to have originated on an island in the Indian Ocean and brought to the area by the movement of people and goods, these invasive marauders arrived around two decades ago and started killing the acacia ants, leaving the whistling-thorn trees vulnerable to herbivores. Diminished tree cover poses a problem for lions because they rely on the element of surprise to ambush their prey, notably zebras.