On three or four occasions while watching foraging wood ants I've seen something that strikes me as a bit odd. Can anyone explain?

It involves three ants, one large and two slightly smaller, which appear to be walking in formation. The large ant leads the way while the smaller ants, one on each side, hold on to one of the larger ants rear legs. There's no sense of struggle and none of the surrounding ants react as I would expect them to if some sort of conflict was taking place. Do ants use physical contact in this way to guide each other? I thought they laid trails by way of chemical messages.

Sorry but no one seems to know the answer to your question.