IMO the ants found an unlimited source of good food! They just got lucky.

I remember a long ago a post about a fire ant nest near a pond & many ants falling in the pond & being eaten. There were some BG deaths.

I like Amdro for fire ants. I would get a bottle of the granules, follow directions & put it around the feeder. Not sure what will happen? If the ants forage they will find the Amdro. If not, I would run the feeder dry, get rid of the ants & start over with a dose of Amdro around the base.

Ants on their own accord may move on when the feeder is empty of food & they have no structure around them as a nest for the Queen, her eggs, & larva.

I enjoy killing Fire Ants!