Bull horn acacia and ants have a mutualistic relationship with many facets: a. large thorns provide nesting for ants, b. Beltian bodies (and nectar) provide food for ants, c. ants swarm to defend anything eating the tree, and d. the ants also clear an area around the base of the tree to reduce competition for nutrients. Artist: Emily Harrington. Copyright: All rights reserved. See gallery for details.
“Some types of acacia trees have evolved special structures to support acacia ant colonies…The orange bodies on the tips of new leaflets are used only to feed the ants. The trees also excrete nectar for ant food and have swollen hollow thorns that can be used for nest sites. In return, the ants, which are equipped with powerful stingers, attack caterpillars and deer and any other animals that try to eat the acacia leaves.
“Some ant-plant partnerships are so strong that the ants live their entire lives within one kind of tree. Bulls horn acacia trees have large hollow thorns that are occupied by skinny, rust-coloured acacia ants. The trees produce not only nectar but also special oil- and protein-rich nodules on their young leaf tips. These provide all the nutrition the ant colony will ever need. To allow the tree better growing opportunities, the ants even trim away weeds from its base.” (Forsyth 1992:52)
Note: Similar relationships occur with other species of acacia, including Acacia drepanolobium.