THE ARMY-ANT BEHAVIOR PATTERN: NOMAD-STATARY RELATIONS IN THE SWARMERS AND THE PROBLEM OF MIGRATION

Abstract

Evidence is reported which indicates that the nomad-statary pattern of colony behavior previously reported for column-raiding army ants also holds for the swarm-raiding species Eciton burchelli. Extensive field records on given colonies of this species disclose a regular parallelism between intra-colony conditions (condition of the brood, in particular) and colony behavior. Evidence is given for. the conclusion that periodic changes in the stimulative (i.e., trophallactic) effect of the brood upon the workers accounts for the regular alternation of nomadic phases (extensive raids; daily colony movements) and statary phases (no colony movements; small raids or none) in the cycle. As in E. hamatum, the basic controlling factor appears to be the reproductive cycle of the single colony queen. Since each given series of Eciton colony movements occurs in a predictable and periodic manner, on an intraorganic (reproductive) basis rather than according to alimentary (i.e., food-scarcity) condition as some authors have claimed, these cycles of movement and rest may be considered a "primitive" or rudimentary instance of migration. Although a reversal of horizontal directionalization apparently is absent in the army ants, there exists a biological equivalent of reversal in the form of an altitudinal shifting of the home site in different phases of the activity cycle.