Confidence: It's likely to be this, but I can't be certain.
Notes: I think it has to be this complex ('F. rufa' as we used to know it is a complex of rufa, polyctena and their hybrid). It is known from this area. It is odd that they are massing like this on a trunk, and I wonder if there is a sap-run to attract them. They nest in thatched mounds, not in tree-trunks.