"Even a worm will turn" is an English language expression used to convey the message that even the meekest or most docile of creatures will retaliate or seek revenge if pushed too far. The phrase was first recorded in a 1546 collection of proverbs by John Heywood, in the form "Treade a worme on the tayle, and it must turne agayne." At the time “agayne” also meant “against” or “oppose”. It was used in William Shakespeare's play Henry VI, Part 3 (Act 2, Scene 2). In the play, the phrase is uttered by Lord Clifford, killer of Rutland as:

It's been proposed that this passage from Henry VI was suggested by one in a history by Edward Halle. In that book the Earl of Warwick makes a speech that includes the passage:

In 1641, the following passage in a letter from from Edmund Verney to his son Ralph Verney further confirms the proverb's meaning that small affronts can lead to rebellion.

The proverb is also found in other countries