Army ant colonies display complex foraging raid patterns involving
thousands of individuals communicating through chemical trails. In
this paper we explore, by means of a simple search algorithm, the
properties of these trails in order to test the hypothesis that their
structure reflects an optimized mechanism for exploring and exploiting
food resources. The raid patterns of three army ant species, {em
Eciton hamatum}, {em Eciton burchelli} and {em Eciton rapax}, are
analysed. The respective diets of these species involve large but
rare, small but common, and a combination of large but rare and small
but common, food sources. Using a model proposed by Deneubourg and
collaborators, we simulate the formation of raid patterns in response
to different food distributions. Our results indicate that the
empirically observed raid patterns maximise return on investment, that
is, the amount of food brought back to the nest per unit of energy
expended, for each of the diets. Moreover, the values of the
parameters that characterise the three optimal pattern-generating
mechanisms are strikingly similar. Therefore the same behavioural
rules at the individual level can produce optimal colony-level
patterns. The evolutionary implications of these findings are
discussed.Postprint (published version
