Fig. 1. (A,B) The experimental arrangements used to train and test the bees. (A) Megachile rotundata. Bees were nesting in holes drilled in the back wall of a wooden box. During training, a shape (termed positive, +ve) was presented on a vertical wall that divided the box into two compartments. To reach the nesting compartment, the bee had to fly though an opening in the centre of the shape. During testing, the positive shape was presented simultaneously with a novel shape, their positions being interchanged at regular intervals. (B) Apis mellifera. At the feeding site, two shapes were presented simultaneously, one rewarding (termed positive, +ve), the other not (negative, –ve). Their positions were interchanged at regular intervals. The tube in the centre of the rewarding shape led to the feeding dish; the other tube was closed. (C) Shapes used to test the bees’ discrimination of edge features were presented as a random-pixel pattern against a similarly patterned background.