Information flow, opinion polling and collective intelligence in house–hunting social insects

Abstract

The sharing and collective processing of information by certain insect societies is one of the reasons that they warrant the superlative epithet 'super-organisms' (Franks 1989, Am. Sci. 77, 138-145). We describe a detailed experimental and mathematical analysis of information exchange and decision-making in, arguably, the most difficult collective choices that social insects face: namely, house hunting by complete societies. The key issue is how can a complete colony select the single best nest-site among several alternatives? Individual scouts respond to the diverse information they have personally obtained about the quality of a potential nest-site by producing a recruitment signal. The colony then deliberates over (i.e. integrates) different incoming recruitment signals associated with different potential nest-sites to achieve a well-informed collective decision. We compare this process in honeybees and in the ant Leptothorax albipennis. Notwithstanding many differences - for example, honeybee colonies have 100 times more individuals than L. albipennis colonies - there are certain similarities in the fundamental algorithms these societies appear to employ when they are house hunting. Scout honeybees use the full power of the waggle dance to inform their nest-mates about the distance and direction of a potential nest-site (and they indicate the quality of a nest-site indirectly through the vigour of their dance), and yet individual bees perhaps only rarely make direct comparisons of such sites. By contrast, scouts from L. albipennis colonies often compare nest-sites, but they cannot directly inform one another of their estimation of the quality of a potential site. Instead, they discriminate between sites by initiating recruitment sooner to better ones. Nevertheless, both species do make use of forms of opinion polling. For example, scout bees that have formerly danced for a certain site cease such advertising and monitor the dances of others at random. That is, they act without prejudice. They neither favour nor disdain dancers that advocate the site they had formerly advertised or the alternatives. Thus, in general the bees are less well informed than they would be if they systematically monitored dances for alternative sites rather than spending their time reprocessing information they already have. However, as a result of their lack of prejudice, less time overall will be wasted in endless debate among stubborn and potentially biased bees. Among the ants, the opinions of nest-mates are also pooled effectively when scouts use a threshold population of their nest-mates present in a new nest-site as a cue to switch to more rapid recruitment. Furthermore, the ants' reluctance to begin recruiting to poor nest-sites means that more time is available for the discovery and direct comparison of alternatives. Likewise, the retirement of honeybee scouts from dancing for a given site allows more time for other scouts to find potentially better sites. Thus, both the ants and the bees have time-lags built into their deci...

Consensus decision making in human crowds

“…Franks et al (2003) found that in house-hunting ant colonies, Leptothorax albipennis, a speedeaccuracy trade-off exists, and that when conditions are benign the ants take longer over their collective decision making to maximize accuracy, whereas when conditions are harsh they must come to a decision more quickly at the expense of accuracy. We did not find a relationship between the speed and accuracy of our groups.…”

“…In some cases, it has been shown that very few individuals within a group may actually possess information on, for example, the direction to a resource (ants, Leptothorax albipennis: Franks et al 2002; honeybees, Apis mellifera: Seeley 2003; golden shiners, Notemigonus crysoleucas (in the laboratory): Reebs 2000; guppies, Poecilia reticulata (in the laboratory) : Reader & Laland 2000;Swaney et al 2001). The simplest situation where such information differences among group members are present could be because of the different spatial positions of individuals.…”

“…Camazine et al 1999;Seeley & Buhrman 1999;Mallon et al 2001;Britton et al 2002;Pratt et al 2002;Couzin & Franks 2003;Franks et al 2003;Seeley 2003;Dornhaus et al 2004;Seeley & Visscher 2004;Pratt 2005) and, therefore, much more is known about the mechanisms behind consensus decisions in eusocial insect colonies than in vertebrate groups. Two particularly well studied and elegant examples involve nest site choice in swarming honeybees, A. mellifera, and the ant, L. albipennis.…”

“…Two particularly well studied and elegant examples involve nest site choice in swarming honeybees, A. mellifera, and the ant, L. albipennis. Scouts locate potential new sites and their recruiting success is dependent on the quality of the new site (honeybees, A. mellifera : Seeley & Buhrman 1999;Seeley 2003;Seeley & Visscher 2004;ants, L. albipennis: Mallon et al 2001;Franks et al 2003). This positive feedback loop ensures that consensus decision can be achieved when the number of scouts recruiting for a particular site reaches a certain threshold (quorum), at which point all individuals leave for the new site Franks et al 2003).…”

Variability in individual assessment behaviour and its implications for collective decision-making

“…Earlier work by Pratt et al [27,38] demonstrated that workers introduced to, or removed from, a new nest site by hand directly influenced other ants' assessments of whether a quorum threshold had been achieved. Thus, individual nest visit durations that are positively associated with overall nest quality, as demonstrated here, may influence quorum attainment at the collective level, both directly via worker presence and indirectly via recruitment decisions, favouring the choice of the highest quality nest site available.…”