Swollen Thorn Acacia Ants

The swollen-thorn acacias are native to Mexico and Central America. In its native habitat, colonies of stinging ants (Pseudomyrmex app.) occupy the hollowed-out thorns and fiercely defend the tree against ravaging insects, browsing mammals and epiphytic vines. In return, the host supplies its little guardian ants with yellow protein-lipid Beltian bodies from its leaflet tips and carbohydrate-rich nectar from glands on its leaf stalk (pit-shaped structure at the base of the leaf stalks). There is no known function for the Beltian bodies, other than to provide food for the symbiotic ants. These species of Central American swollen-thorn acacias lack the chemical defenses of most other acacias to deal with their predators and competition. Without bitter alkaloids, ravaging insects and browsing mammals eat the leaves and branches, slowing the growth of the acacias and allowing fast-growing, competing vegetation to shade them out. Symbiotic ants have taken over this vital defense role, protecting the acacia from hungry herbivores and pruning away competing plants. The ants live inside the inflated thorns at the base of leaves.