Ants Are at the First Stage of the Notion of Zero

The notion of zero is rarely apprehended by animals. We examined if ants possess this ability in four experiments, each time using two colonies and operant conditioning. Ants succeeded in significantly comprehending the absence of a cue, but not as well as learning an existing cue, and they soon lost their learning. Ants thus have a sensory notion of the absence of an item, but not the abstract notion of a sensu stricto mathematical zero.