busy little beaver

A very busy, assiduous, or hardworking person. Taken from the phrase "busy as a beaver," referring to beavers' reputation for being extremely industrious. Between working two part-time jobs, volunteering on the weekends, and looking after his brother, Sam's been a busy little beaver this summer. I've been a busy little beaver this year. I've had almost no free time! Believe me, we've all been busy little beavers working on this audit. We can't wait till it's over!