Mad as a March Hare

A genuinely observed piece of natural history turned into idiom. Hares are usually shy, solitary animals, but during their spring breeding season, roughly centred on March, they engage in dramatic "boxing" matches, leaping, chasing, and striking each other with their front paws, most often females fending off overeager males. To anyone watching without knowing why, it looks exactly like sudden madness. The comparison is recorded from around 1500, in the poem Blowbol's Test, and was already established enough to be included in John Heywood's collection of English proverbs in 1546. Lewis Carroll's March Hare character in Alice in Wonderland (1865) drew directly on this already-centuries-old phrase.