In spite of their bare exterior, these thorns are full of life. My favorite kind of life, in fact. Ants!
The relationship between Tetraponera and tree is complex. The Acacia hosts several other ant species, notably Crematogaster acrobat ants, and the different species have different effects on their host plant at different stages in the tree’s life, sometimes beneficial, sometimes not. The system is an ecologist’s dream (or nightmare, depending on your perspective), and has generated an impressive technical literature attempting to untangle the nuances.