Comment by DrScientist

Ants also farm other insects.

For example often if you have a blackfly infestation, the first sign is often a steady stream of ants - they are feeding of the honeydew created by the blackfly, they protect the blackfly from predators like ladybird larvae, and they will even transfer the blackfly to new plants.

Once I knew this I found the best way to tackle blackfly was not to go after the blackfly, but distract the ants - a bit of jam works a treat.

Though you could then argue the ant's have then moved on, from farming, to a protection racket.