Features

• The swollen-thorn acacias have large, hollow thorns that act as homes for stinging ants in the genus Pseudomyrmex. The ants remove fungal spores, kill small herbivores, and destroy any plants or vegetation growing too close to the acacia tree. In return, the tree provides nectar for the ants.
  
  

Function

• The relationship between the ants and the tree is a remarkable example of what ecologists call mutualism, meaning an interaction between two species that benefits both. The ants earn shelter and food, while the acacia gains protection from herbivores and competitors.
  
  

Considerations

• While some swollen-thorn acacias enjoy mutualistic relationships with ants, not all of them do. The relationship between the African whistling thorn acacia and its ants, for example, is less than completely mutualistic, because the ants can actually harm this particular tree. Unlike other acacias, the whistling thorn doesn't provide food for the ants, so they must forage farther afield, and the ants make no attempt to fend off small herbivores--indeed, they may even tend scale aphids that feed on the tree so that they can use the aphids for food.