Autumnal mass migrations of spiny lobsters, Panulirus argus, involve diurnal movements of thousands of individuals in single-file queues. Initiation, posture, and alignment of a queue can be effected entirely by tactile cues received through antennular inner rami, pereiopods, and antennae. Since spiny lobsters queue when deprived of shelter, this behavior may serve a defensive function. Specimens captured while migrating maintain the queue indoors for up to several weeks, whereas at other times the queue lasts only a few hours. Hence, the migratory behavior probably depends in part upon environmentally induced neurohormonal changes.