The production of behaviour that is a direct consequence of the effects produced in the local environment by previous behaviour. For example, when termites (Isoptera) start to build a nest, they modify their local environment by making little mud balls, each of which is impregnated by a pheromone. Initially the termites deposit their mud balls at random. The probability of depositing one on top of another increases as the sensed concentration of pheromone increases. After the first few random placements, the other termites tend to deposit their mud balls in the same place, so that small columns are formed. The pheromone from neighbouring columns causes the tops of the mud columns to lean towards neighbouring columns, Eventually the tops meet, forming arches, the basic building units of the nest. As other stigmergic rules come into play, involving water vapour, carbon dioxide concentration, and the presence of the queen, the whole complex nest structure is produced. This may include the royal cell, brood nurseries, air conditioning, larders, and communication tunnels.
The essence of stigmergy is that simple behavioural rules change the environment in such a way that new rules are triggered by the new environmental stimuli. Thus the behavioural repertoire becomes self-organizing. This is the principle behind much of the social behaviour of ants (Hymenoptera) and termites.
Subjects: Zoology and Animal Sciences.