Colonies of P. metricus were collected from the field and maintained in the laboratory. Pupae that were destined to become workers were excised from nests and isolated individually. Upon eclosion, workers were exposed to either an untreated fragment of the natal nest, to a fragment of the natal nest from which the surface hydrocarbons had been removed with hexane, or to no nest fragment. Four days after emergence, each wasp was released into an observation box which contained a nest fragment from her own nest and a nest fragment from a foreign nest. Each wasp was observed for 30 min on the first day and 30 min on the second day, and the time that the wasp spent on the nest fragments was recorded. P. metricus workers that had emerged on an untreated nest fragment spent significantly more time on the natal nest fragment than on the foreign nest fragment. Workers that emerged in the absence of a nest fragment spent less time on either nest fragment than did the wasps that had emerged in the presence of a fragment of their natal nest. This is the first report to document the importance of prior exposure to nest paper hydrocarbons for social wasps to be able to discriminate between their natal nest and a foreign nest.