Wood ants express uncertainty when engaging with magnetic cues for directional guidance

Abstract

Wood ants were trained indoors to follow a route in a chosen magnetic direction from the centre of a small, circular arena to find a drop of sucrose at the edge. The arena, surrounded by a white cylindrical wall, was in the centre of a 3D coil system that generated an inclined Earth strength magnetic field in any horizontal direction. Between trials, the chosen magnetic training direction was rotated to a new orientation. Tests were given without food and with fresh or reversed paper on the floor of the arena. In a significant number of tests, ants left the centre facing the goal, or in the opposite direction, but they mostly failed to reach the goal. Tests given early in the day, before any training, show that ants remember the magnetic route direction overnight. On some training trials, the position of the sucrose was also indicated by a black stripe. Not uncommonly, ants first moved in the opposite direction to the stripe before switching to the correct direction. Travel away from the reward seems to express the ants uncertainty about the correct path to take. Tests show that this uncertainty may stem from competing directional cues linked to the room, suggesting that ants are reluctant to rely on magnetic information alone. We conclude that ants can remember a route direction defined by an Earth-strength magnetic field and that they express any uncertainty about the correct direction by moving for a stretch in the opposite direction. In a second experiment, an upright and an inverted triangle were fixed 90{degrees} from each other to the inside of the cylinder. Sucrose was placed beneath one of the triangles, dependent on the direction of the magnetic field. Ants failed to master this task and to approach the magnetically cued triangle. Instead, they preferred to approach the upright triangle. The ants were again uncertain of the correct direction and expressed this uncertainty through paths that had segments directed towards both the inverted and the upright triangles.