Pheromones are important cues for social insects such as ants. As a first step in elucidation of pheromonal information processing mechanisms in the myrmicine ant, we investigated the morphological structure of the antennal lobe. Using autoflourescence imaging, labeling of neuronal filamentous actin, and reduced silver impregnation staining, the antennal lobe was found to consist of five compartments that, each received input from a different antennal sensory tract. Two major tracts of projection neurons, the medial and lateral antenno-cerebral tract (m- and l-ACT), originated from a different region of the antennal lobe. The in-ACT originated from the posterior part of the antennal lobe whereas the I-ACT originated from the anterior part. These results demonstrate a spatial segregation of function within the antennal lobe.