Acacia-ant symbiosis is the interaction between myrmecophilous Vachellia trees and ants that nest on them. Obligate acacia ants dwell in the gall-like domatia within the swollen stipular spines of African or Central American ant acacia species, and they also take the food offered by the tree. Some of them protect ant acacias from herbivores in return, hence mutualism; the others provide inadequate protection or none at all, hence weaker or non-mutualism. Facultative (non-obligate) acacia ants often nest on stems instead of in gall-like domatia, and tend to be non-mutualistic.