Brewer's: Hares shift their Sex
It was once thought that hares are sexless, or that they change their sex every year.
“Lepores omnes utrumque sexum habent.”
Snakes that cast their coats for new, Cameleons that alter hue, Hares that yearly sexes change.
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894