The blind leading the blind in army ant raid patterns: Testing a model of self-organization (Hymenoptera: Formicidae)

Abstract

We présent field experiments and analyses that test both the assumptions and the prédictions of a model that showed how the swarm raids of the army ant Eciton burchel l i might be selforganizing, i.e., based on hundreds of thousands of interactions among the foraging workers rather than a central administration or hierarchical control. We use circular mill experiments to show that the run ning velocity of the ants is a sigmoidal function of the strength of their trail pheromones and provide évidence that the swarm raid is structured by the inter action between outbound and inbound forager traffic mediated by the phero mones produced by both of thèse sets of ants. Inbound traffic is also affected by the distribution of prey, and hence, sites of prey capture alter the geometry of the raid. By manipulating the prey distributions for E. burchel l i swarms, we have made them raid in a form more typical of other army ant species. Such selforganization of raids based on an interaction between the ants and their environment has profound consé q uences for interprétations of the évolution of army ant species.

Emergent oscillations assist obstacle negotiation during ant cooperative transport

“…Rather, the constraint directly affects the group as a whole, transitioning it into a collective state that promotes the solution of the problem. Such emergent responses to environmental conditions are reminiscent of those observed in the context of ant trail formation (31,32) and nest construction (33).…”

Social behaviour and collective motion in plant-animal worms

“…At the outset of modern studies of collective decision-making, circular milling behaviour was seen as a key characteristic of ultracohesive group movement [10]. It has been reported, for example, in Bacillus bacteria [12,13], Daphnia [14], processionary caterpillars [15], army ants [16], fish [17,18] and tadpoles [19].…”

“…Indeed, circular milling seems often to be maladaptive, especially in processionary caterpillars and army ants where individuals may remain trapped in a mill, by more and more trail laying, until they die of exhaustion [16]. In fish, where it occurs fairly frequently, it may serve for predator avoidance [20] through an extreme form of the geometry for the selfish herd [24].…”

“…In processionary caterpillars and army ants, circular milling is underpinned by individuals laying trails that others follow and reinforce [15,16]. In fish, it occurs because of rules of attraction and alignment [11,[20][21][22].…”

Ants estimate area using Buffon's needle

“…How the behaviour of individual workers translates into collective decisions by the whole or large parts of a colony is now a major area of interest in the study of social insects (Franks 1989;Beckers et al 1993;Bourke & Franks 1995;Seeley 1995;Bonabeau et al 1997;Detrain & Deneubourg 1997;Pratt 1998;Detrain et al 1999). However, relatively little work has been done on the information gathering which provides the options for these decision-making processes (but see Seeley 1977;Lumsden & HÎlldobler 1983;Beckers et al 1990Beckers et al , 1992Franks et al 1991).…”