Nature
Honeybees can rank zero as a number, not just recognise 'nothing'
Trained to always pick the image with fewer dots, honeybees offered a real choice against a blank card chose the blank — placing zero below one on a number line, something previously shown only in a few primates and an African grey parrot. Their brains hold under a million neurons, yet they grasped an abstraction humans took millennia to formalise.