Mutualism.
Some acacia trees have hollow thorns that house stinging ants which
feed on sugar secreted by nectaries and on protein–rich swellings.
The acacia benefits because the ants attack anything that touches the tree.
Ants can also be mutualistic with
fungi
and
caterpillars.
Other examples include mycorrhizae
, cleaner
shrimp
and
gobies
,
and Clownfish/Anemone
relationships.