work like a beaver
Also, work like a dog or horse or Trojan. Work very energetically and hard, as in She worked like a beaver to clean out all the closets, or I've been working like a dog weeding the garden, or He's very strong and works like a horse. The first of these similes is the oldest, first recorded in 1741; the variants date from the second half of the 1800s. Also see work one's fingers to the bone.
Dictionary.com presents 366 FAQs, incorporating some of the frequently asked questions from the past with newer queries.