In return, the host supplies its little guardian ants with protein-lipid Beltian bodies from its leaflet tips (yellowish granules in photo) and carbohydrate-rich nectar from glands on its leaf stalk (volcano-shaped structure just above pair of thorns). There is no known function for the Beltian bodies, except to provide food for the symbiotic ants. Unlike other acacias, Bullhorn acacias are deficient in the bitter alkaloids usually located in the leaves that defend against ravaging insects and animals. Bullhorn acacia ants fulfill that role.

The ants act as a defense mechanism for the tree, protecting it against harmful insects, animals or humans that may come into contact with it. The ants live in the hollowed-out thorns for which the tree is named after. In return, the tree supplies the ants with protein-lipid nodules called Beltian bodies from its leaflet tips and carbohydrate-rich nectar from glands on its leaf stalk. These Beltain bodies have no known function other than to provide food for the symbiotic ants. The aggressive ants release an alarm pheromone and rush out of their thorn "barracks" in great numbers.

According to Daniel Janzen (Costa Rican Natural History, 1983), livestock can apparently smell the pheromone and avoid these acacias day and night. Getting stung in the mouth and tongue is an effective deterrent to browsing on the tender foliage. In addition to protecting A. conigera from leaf-cutting ants and other unwanted herbivores, the ants also clear away invasive seedlings around the base of the tree that might overgrow it and block out vital sunlight.