Vachellia drepanolobium

Vachellia drepanolobium (syn. Acacia drepanolobium), commonly known as Whistling Thorn (family Fabaceae), is a swollen-thorn vachellia native to East Africa. The whistling thorn grows up to 6 meters tall. It produces a pair of straight thorns at each node, some of which have large bulbous bases. These swollen thorns are naturally hollow and occupied by any one of several symbiotic ant species. The common name of the plant is derived from the observation that when wind blows over bulbous thorns in which ants have made entry/exit holes, they create a whistling noise.