Green’s Dictionary of Slang

eager beaver n.

[the ever-industrious beaver]

(orig. US) an excessively earnest, keen person whose efforts are sometimes more notable for their sound and fury than their actual usefulness.

[US]M. Hart Winged Victory I ii: They march off—six very, very eager beavers.
[Aus]Aus. Women’s Wkly 8 July 3/3: Don’t be an eager beaver.
[US]J. Thompson Getaway in Four Novels (1983) 74: Some eager beaver of a lab hound had managed to raise a latent print on the man’s corpse.
[US]J.P. Donleavy Fairy Tales of N.Y. I i: O.K. You don’t mind if we wait a few minutes. Until some of these eager beavers get off this pier.
[US](con. 1945) E. Thompson Tattoo (1977) 270: A couple of eager beavers began to chip once more.
[Aus]B. Robinson Aussie Bull 7: In every job there are those who ‘wouldn’t work in an iron lung’, the ‘whingers’, the ‘practical jokers’, the ‘quiet achievers’, and the ‘eager beavers’.
[US]L. Heinemann Paco’s Story (1987) 22: The captain was antsy anyway, a real eager beaver.
[US]J. Stahl Permanent Midnight 284: Eager beaver that I was, I wanted to hop right behind that counter.
B. Hughes Lighter Side of Firefighting 94: Eager Beaver A volunteer fire department had just bought a new ladder truck for their recently built fire hall. One of the eager guys on the squad jumped behind the wheel [etc].
[US] N. Flexner Disassembled Man [ebook] ‘I need to see her. Soon.’ ‘Well, well, well. You’re quite the eager beaver’.
[US]A. Kirzman Giuliani 162: [H]e was out on the streets working as a ‘barker,’ beseeching pedestrians to come meet the candidate. The eager-beaver attitude paid off.
[UK]M. Herron Secret Hours ‘I said, you bucking for a promotion, Sir Winston? [...] Because you’re certainly the eager beaver today’.