Two sympatric species of hermit crabs, Calcinus haigae and Calcinus hazletti, appear to have different microhabitat distributions in the subtidal. Several biotic factors may be influencing this microhabitat difference. We documented the field distributions of these two species as a function of coral species and investigated whether aggregation behavior, avoidance behavior, and/or shell exchanges are influencing the distribution patterns. Individuals of C. hazletti occurred predominantly on the cauliflower coral Pocillipora meandrina. In addition, individuals of C. hazletti aggregated toward conspecifics in the laboratory. Individuals of C. haigae avoided individuals of C. hazletti in the field unless the C. haigae were in damaged shells. Individuals of C. haigae did not initiate interspecific shell exchange attempts in the laboratory, but individuals of C. hazletti did initiate interspecific shell exchanges. Thus, both intraspecific and interspecific interactions affect the distributions of these crabs.