Competition for food and aggregating behavior were examined in plains garter snakes (Thamnophis radix), in 11 groups of 1 noncompetitor and 2 competitors. Aggregation data were obtained in 48 daily scans. During food competition, success at obtaining food was asymmetrical across pairs. For aggregation, competitors were mostly associated with noncompetitors. After removal of noncompetitors, competitors were more likely to be solitary, but associations between competitors increased. After a 5-month separation, 5 of the original groups were reconstituted; aggregation patterns similar to the 1st experiment were observed. In a 3rd experiment, unfamiliar animals with and without competitive experience did not aggregate preferentially. Garter snakes discriminate on the basis of sex and species; in this study individual relationships (prior competition) affected aggregation, and the data suggest individual recognition both occurs and persists over time.