A review of body odor-mediated behaviors of hermit crabs, predatory gastropods, barnacle larvae and brachyuran crabs includes a model based on the hypothesis that all the behaviors are mediated by a similar chemical detection mechanism. A key assumption is behaviors evolved due to a selective advantage conferred by detection of information in body odors. In the model, exogenous trypsin-like proteases digest structural proteins to generate neutral-basic peptides. The receptor is postulated to have resulted from a point mutation in a trypsin-like membrane protein. Transduction of the binding event is via second messenger mediated pathways. Examples of body odors functioning as cues, allomones and pheromones are presented. The model is supported by a review of structure-function studies employing synthetic neutral basic peptides and studies with other macromolecules. © 1993 by the American Society of Zoologists.