an eager beaver
One who is industrious and enthusiastic (perhaps annoyingly so). Give that big project to the new girl, she's a real eager beaver. Aren't you an eager beaver, getting to the office an hour early.
an eager beaverINFORMAL
If you describe someone as an eager beaver, you mean that they are very enthusiastic about work and want very much to please other people. There are always eager beavers, people who stay behind after the talk to ask penetrating questions. Ed was the first to arrive at the office, the eager beaver! Note: Eager-beaver can also be used before a noun. If fraud became an issue, he might interest an eager-beaver lawyer in the case. Note: You usually use these expressions to show that you find someone's behaviour foolish or annoying. Note: Beavers are often associated with hard work, as they spend a lot of time building shelters and dams (= walls across rivers) out of mud and wood.