ABSTRACT.Considerable differences were found in the composition of the volatile cephalic chemical of the castes ofOecophylla longinoda.The mandibular glands of minor workers contain a series of primary alcohols, predominantly 1‐hexanol, 1‐octanol and 1‐nonanol, together with nerol and geraniol. Hexanal, 2‐butyl‐2‐octenal and 3‐undecanone (components of the mandibular gland secretion of major workers, and which are important stimuli in alarm communication) are absent. Major workers are attracted and arrested by high concentrations of nerol, which is part of a possible mechanism for communication within the nest. The heads of males contain a pungent secretion, which may be used in defence; the major constituents are five aliphatic acids. The quantities of both main and trace constituents of the mandibular gland secretion of major workers were found to vary between colonies collected in different areas o