Acacia
One of four different species of ant lives in each of these igloos, which they open up by cutting holes into them. A dying bush whistles as the wind blows over these entrances. Most acacias make toxins that it rushes to leaves that are under attack by browsers. The whistling thorn does not. It is infested with stinging ants that swarm out and prepare to bite anything they can when the branch is disturbed. Most browsers seem to avoid infested bushes, perhaps because the ants stink of formic acid.