I have heard about ants farming aphids and I am assuming that this is what is happening here - it was fascinating to see.
I checked with google as well:
'Some species of ants farm aphids, protecting them on the plants where they are feeding, and consuming the honeydew the aphids release from the terminations of their alimentary canals. This is a mutualistic relationship, with these dairying ants milking the aphids by stroking them with their antennae.'
These are cashew nuts - I was intrigued how the fruit is the same shape as the cashew nut inside.
