even a worm will turn

First attested in a collection of proverbs by John Heywood in 1546, in the form “Treade a worme on the tayle, and it must turne agayne.” Popularized by William Shakespeare in The Third Part of Henry the Sixth, see quotations.

even a worm will turn

1. Even the meekest or most docile people will retaliate or seek revenge if pushed too far.
   • c. 1591–1592 (date written), William Shakespeare, “The Third Part of Henry the Sixt, […]”, in Mr. William Shakespeares Comedies, Histories, & Tragedies […] (First Folio), London: […] Isaac Iaggard, and Ed[ward] Blount, published 1623, →OCLC, [Act II, scene ii], page 154, column 1:

     The ſmalleſt Worme will turne, being troden on, / And Doues will pecke in ſafegard of their Brood.

     The smallest worm will turn, being trodden on, and doves will peck in safeguard of their brood.

• even a worm will turn on Wikipedia.Wikipedia