Agonistic Behavior of the Blue Crab, Callinect Us Sapid Us Rathbun

Behavior patterns of blue crabs (Callinectes safridus) were observed in both field and laboratory. Most agonistic acts employ the chelipeds, which can serve as organs of expression as well as weapons. They are spread in threat, used to ward off or grasp an opponent, or folded in crouching, which appears to be a submissive gesture. These acts serve to halt the approach of other individuals or to cause them to withdraw. Vigorous combat was seen only when they failed to deter crabs that were attracted to food or a sexually receptive female held by another individual. 2. Differences were found in the distances between crabs at which various agonistic acts occurred. The responses by crabs to individuals that were approaching differed with their own orientation and with that of the approaching animal. The frequency distribution of the various acts also differed with the size and sex of the crabs, and with the presence of food or a receptive female. 3. Presentation of a model of an adult male crab to captive animals showed that agonistic responses differed with the speed of approach, orientation, cheliped posture and distance of the model, and with the sex and size of the crabs. Animals responded to the model more often when it approached rapidly, frontally or with extended chelipeds than when it approached slowly, laterally or with folded chelipeds Females responded to the model more often than did males, and smaller individuals similarly responded more often than did larger ones. In cases where animals responded more frequently, they typically extended their chelipeds, crouched or withdrew from the model.