Seasonal patterns in the orientation system of the migratory ant Pachycondyla marginata

Route directions of migrations by the neotropical termite-hunting ant Pachy condyla marginata at a forest reserve in Southeast Brazil were analysed by circular statistic. Colony movement patterns were compared between the rain y/hot and dry/cold seasons. Migrations during the dry/cold season are signi ficantly oriented 13 degrees with the magnetic North-South axis, while rain y/hot migrations do not exhibit a preferred direction. This result is discu ssed considering the hypothesis that P. marginata ants may use the geomagne tic field as an orientation cue for migrations in the dry/cold season. The presence of magnetic iron oxides in the head and abdomen of P. marginata is consistent with this suggestion.