Multiple stored views and landmark guidance in ants

Under some circumstances, Diptera and Hymenoptera learn visual shapes retinotopically, so that they only recognize the shape when it is viewed by the same region of retina that was exposed to it during learning(1,2). One use of such retinotopically stored views is in guiding an insect's path to a familiar site(3-5). Because the retinal image of an object changes with viewing distance and (sometimes) direction, a single stored view may be insufficient to guide an insect from start to goal. Little, however, is known about the number of views that insects store. Here we show that wood ants take several 'snapshots' of a familiar beacon from different vantage points. An ant leaving a newly discovered food source at the base of a landmark performs a tortuous walk back to its nest during which it periodically turns back and faces the landmark The ant, on revisiting the familiar landmark, holds the edges of the landmark's image steady at several discrete positions on its retina. These preferred retinal positions tend to match the positions of landmark edges that the ant captured during its preceding 'learning walks'.