From what I can tell these guys were harvester ants. I snapped this photo at the lavender festival at Blanco by the side of the road where the booth was located. They didn't seem to bother anyone, the little black ants did more of that.
I tossed a few pebbles on top to see how many would come out and defend the mound, not big pebbles mind you, just big enough to get their attention. Not many did but besides horned lizards I don't think many things mess with them.
I didn't see them bringing anything into the mound the ants mostly sat there and guarded the entrance. I guess it's the slow season for them.