Social insect colonies typically have well-defined social and physical boundaries but in some cases, colonies may take-on a more diffuse form with no obvious nestmate recognition or inter-colony aggression. Why colonies adopt closed versus open societies is not well understood, but it is presumably related to the genetic or environmental identity of individuals. In this study, we use Canadian populations of the Eastern subterranean termite (Reticulitermes flavipes) to test for evidence of aggression and nestmate recognition. Specifically, we predict that any inter-colony aggression will increase as a function of geographic distance. In short-term, (5-min) Petri-dish trials (varying caste, group size and colony source) we observed no evidence of aggression. However, in 2- and 7-day shared-resource assays, we observed very little inter-colony mixing and a high incidence of mortality in non-nestmate pairings. Our long-term observations imply that subterranean termites sort and potentially compete on the basis of nest origin, and that this recognition is mediated in part by ecological context. This behavior would not be evident from Petri dish-style assays, which lack this context and may explain why prior studies of kin or nestmate recognition in R. flavipes have yielded mixed results.