The bullhorn acacia (Acacia cornigera) is a swollen-thorn acacia tree native to Mexico and Central America that lacks the chemical defenses of most other acacias to deal with competing species and predators. To compensate as a defensive, symbiotic stinging ants (Pseudomyrmex ferruginea) protect the acacia from ravaging insects, browsing mammals and epiphytic vines. This relationship extends to the acacia proving not only shelter for the ants in its thorns but also sweet nutrients and special high quality food nodules from leaf tips for the ants larvae to consume. The ant larvae even have special pouches for the capsules. An impressive symbiosis coexists between the ants and acacias where they are entirely dependent upon each other for survival.


 Bullhorn Acacia Tree - Image by Nikki Davies



The medium sized bullhorn trees are up to 15 meters (45 feet) high that grow protruding, hollow, swollen thorns (stipular spines) which are grouped in pairs at the base of the leaves and point in opposite directions, resembling the horns of a bull. As the acacia tree matures the queen ant digs a hole to the base of the thorns and lays eggs. Once born and fully developed the worker ants leave their thorns daily and patrol the acacia stem and young leaves. These stinging ants hunt down any insect or browsing herbivores that dare to consume the acacias young fresh leaves and attack aggressively. It is quite common that two different colonies of stinging ants meet on the same tree. The stinging ant colonies fight and the largest colony is often able to overrule and claim the entire tree. The ant colonies do not just fight for territorial dominance they also fight for the food the tree provides.