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I saw this solitary ant climbing up the trunk of a cherry tree. I interrupted its progress briefly before it was out of range and it then continued inexorably upwards. The tree was just coming into leaf and flower, so an initial guess that this ant might be scouting for food and setting up a potential pheromone trail for other ants to follow. (It ignored a side branch with flowers on it and carried on upward). It will be of interest to see if a succession of ants goes up and down the tree in days to come.
In the close-up shot the ant appears bicoloured, which would indicate probably Lasius brunneus, but in the other shot it seems uniformly brown, which would indicate L. niger/platythorax. Lighting effects can play tricks. It is not a Formica though.
Lat/Lng: 51.4337, -2.7624
OS grid ref: ST470707