Today (11 January 2014) I turned over some fallen tree limbs on a small patch of chalk grassland on the edge of the Chilterns, and was surprised to a few actively moving workers of Formica fusca. The books I have don't seem to say much about winter activity in worker ants, and John Pontin's "Ants of Surrey" suggests that Formica spp. don't normally have over-wintering workers. Is it unusual to find these? We've certainly had a mild winter here so far, and there was still some warmth in the afternoon sun.