Green’s Dictionary of Slang

1. (US) a special agent of the US Post Office [‘so-called because one of the agents about 1845 chewed off the ear of an opponent in a fight’ (Craigie, Dict. of American English, 1944)].

1855

J. Holbrook Among the Mail Bags 27: How much the result of this first investigation, after the restoration of the ‘ear-biters’ (as they were then sometimes facetiously called,) had to do with the radical change in opinon and action [etc.] [DAE].

2. a cadger, one who seeks constantly to borrow money [bite someone’s ear under ear n.¹ ].

1898		Binstead & Wells A Pink ’Un and a Pelican 264: [chapter heading] Ear-biters at the railway station.
1939		K. Tennant Foveaux 172: Jordan’s many years in a bar had given him a perfect technique in dealing with ear-biters.