The bulging bases on the thorns of the whistling thorn acacia. A number of black ants, that the plant has a symbiotic relationship with, can be seen. 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. Photographed in Tanzania in October
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