Activity in the nest was affected by cloud cover. Outside activity that involves feeding occurs at twilight. Obviously, they are feeding during these short intervals to avoid predators: most animals that eat ants would be inactive at twilight.
Tests were done at ANU in Canberra. Bull ants were put in containers where diffused light was altered. It was found they only fed when the light was set at a particular low level. Evolution does take some winding paths. This shows though that evolution develops in a rational way.