Thank-you for your thoughts. I think there must be a nest somewhere close by. But not sure if they travel a distance to come in contact with ant powder. All other insects seem to be ok in garden. It is possible that they are coming up plug hole I know spiders do this. But it seems along journey up from drain to die like lemmings on my draining board. They are only there in morning that may be, because not using sink then. Kitchen window is double glazed (as is back door) the window ledge + back of sink is tiled so no sawdust. DH is going to dismantle sink cupboard on saturday if they are still there it will be one week of dead ants, but I guess there will be hundreds of ants to a nest!. I have designated my kitchen as a crumb free zone.