Trail following in Two Species of the Army Ant Genus Eciton:1 Comparison between Major and Intermediate-Sized Workers2

Abstract

Colonies of the neotropical army ants Eciton hamatum (F.) and E. burchelli (Westwood) have worker populations that are polymorphic. Major workers, with their huge heads and long, ice-tong-shaped mandibles, exhibit certain behavior patterns with greater frequency than do the smaller workers. The readiness with which major workers leave raiding and emigration trails and approach sources of disturbance is particularly significant. It was hypothesized that the major workers arc less responsive than smaller workers to the chemical trail and correspondingly more responsive to the mandibular gland (or alarm) pheromone. This experiment tested part of the hypothesis by comparing the trail-following performance of major and intermediate workers. The results showed that there are few significant differences in their performance on the chemical trail. As a result, it is hypothesized that the secretion of the alarm pheromone by workers at sites of disturbance probably attracts the major workers off the chemical trail.