Are the food needs seasonal? I asked. 
Yes, to a certain extent, said the pest advisor at Kiwicare. In summer the colony needs more carbohydrate so the workers can fuel their busy lives. But Argentine ants (which mine could be) like protein when they first move in to new territory, then change to carbohydrate once they’ve settled. I guess somewhere behind the wall they must have settled in pretty thoroughly, because they they are turning their little black noses up at my protein baits.