The ability of Apterostigma collare workers to differentiate their nest from other nests and their nestmates from non-nestmates was examined. In field tests, workers that were removed from their nest were accepted back into their own nests, but were rejected when they were placed onto a nearby (≤ 1 m) nest or a distant (≥ 100 m) nest. In the laboratory, when given a choice between a fragment of their own nest and a fragment of a second nest (near or distant), workers selected their own nest material rather than the material of the second nest. For the nestmate recognition bioassay, two workers from one nest were placed together in an arena with a worker from a second nest. In most bioassays, the nestmates were tolerant of each other, but they were intolerant of the non-nestmate. The results demonstrate that A. collare workers have the ability to recognize nestmates and their nests. The results also suggest that each nest of A. collare is an independent colony.