In the savannas of Eastern Africa, ants live in the thorny, hollow bulbs of acacia trees and feed on the trees’ nectar. The ants also act as bodyguards, defending the trees from hungry elephants and giraffes by biting and stinging them. Now, an invasive species known as the bigheaded ant is killing the native ants.

The findings appear in the journal Ecology. The native ants put up a brave fight, streaming out of the acacia trees to meet the invaders, but the invasive species usually wins in a hostile takeover of the trees, said Corinna Riginos, an ecologist at Teton Research Institute and one of the study’s authors. “There are body parts strewn everywhere,” she said.

The bigheaded ants, Pheidole megacephala, stay a while in the acacia trees before returning to their nests, preventing native species from recolonizing the trees.

The researchers report that as a result, the rates of elephant damage to trees in invaded areas is five times higher than in areas where native ants reign.