Metricus paper wasps ( Polistes metricus; left top) at the University of Michigan have been trained to recognize the individual faces of a related species, the golden paper wasp (Polistes fuscatus), to avoid potential pain. Naturally, P. metricus lacks individual recognition, even among its own nest mates. With the lack of individual color variation and solitary nesting behavior of P. metricus, there has been no evolutionary need for recognition behavior to develop. This is in stark contrast to P. fuscatus (left bottom), whose unique facial patterns and communal nesting reinforces the need for individuals to recognize one another for continued cooperation. Each adult P. fuscatus’ face has a specific pattern, making each wasp uniquely recognizable. By raising individuals of these 2 species together, the normally oblivious P. metricus has gained the ability to not only recognize specific wasp faces, but to associate individual P. fuscatus images with pain and actively avoid them.