Ant farm?

Are my dahlias in danger or will the ants take care of the pests? Is this an ants' farm of aphids? Do I need to spray the lot with soapy water? Found on the stem of my dahlias today just now the buds are starting to develop. This is the best shot I could do handheld squatting.

In other news the guest room is ready and my mother is on her way :-)
It's a bit of a standing joke in the family that when there's an important football match my mother will probably call right in the middle of it. This time she has done even better, arriving at the airport in the middle of the opening game of the World Championship :-) I know she didn't plan this on purpose

Thanks very much for your comments on yesterday's Tutsan Blip, isn't nature fascinating !