Vachellia drepanolobium

Vachellia drepanolobium, more commonly known as Acacia drepanolobium or whistling thorn, is a swollen-thorn acacia native to East Africa. The whistling thorn grows up to 6 meters tall. It produces a pair of straight spines at each node, some of which have large bulbous bases. These swollen spines 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 spines in which ants have made entry and exit holes, they produce a whistling noise.

Whistling thorn is the dominant tree in some areas of upland East Africa, sometimes forming a nearly monoculture woodland, especially on "black cotton" soils of impeded drainage with high clay content. It is browsed upon by giraffes and other large herbivores. It is apparently fire-adapted, coppicing readily after "top kill" by fire.

Whistling thorn is used as fencing, tool handles, and other implements. The wood of the whistling thorn, although usually small in diameter, is hard and resistant to termites. The branches can also be used for kindling, and its gum is sometimes collected and used as glue. The ability to coppice after cutting make it a possibly sustainable source for fuel wood and charcoal. Conversely, whistling thorn also has been considered a weed of rangelands, and a bush encroachment species.