Green’s Dictionary of Slang

1. (orig. US) anyone who hangs around wharfs, looking out for an opportunity to steal from a cargo.

1836		Chester Chron 30 Dec. 4/1: A Yankee malcontent [...] I’ve an idea, my man, that you’re one of the wharf rats; and, if so, the less lip you give me the better.
1857		Dundee, Perth & Cupar Advertiser 23 June 2/1: [from N.Y. Tribune] Thousands of lottery dealers, policy backers, pickpockets, hall thieves, burglars, wharf-rats, area sneaks, pimps and vampyres, practice their knaveries openly.
1868		J.D. McCabe Secrets of the Great City 113: Nearly two thirds of the boys have been boot-blacks, the remainder mostly what are technically known as ‘wharf rats.’.
1871		L.H. Bagg Four Years at Yale 49: Wharf rat, a young waterside Arab.
1879		Shields Dly Gaz. 22 May 4/1: The Wharf Rats of New York [...] Wharf-thieves used to be more successful than they are now.
1882		Sydney Sl. Dict. (2 edn) 8: Toshers - ‘Wharf rats’ who steal copper and dunnage from ships.
1883		‘Mark Twain’ Life on the Mississippi (1914) 500: His clothes differed in no respect from a ‘wharf-rat’s,’ except that they were raggeder, more ill-assorted and inharmonious.
1902		Bulletin (Sydney) 5 July 12/2: There was a wild and woolly time amongst the Melbourne unemployed and the wharf-rats and Yarra-bank troglodytes when beer and champagne were distributed freely to the push and its wives and aunts for the honor and glory of King Ned.
1902		N.Y. Eve. World 8 Jan. 5: [cartoon] What’s the matter with ‘Wharf Rat’ Finnigan? Didn’t he get his turkey?
1915		Eve. Public Ledger (Philadelphia, PA) 30 July 8/3: [headline] Wharf Rats Defy Cop to Swim in Delaware.
1920		Barron Harper’s Pictorial Library of the World War X 347: His duties brought him into close relations with sailors, tug-captains, wharf-rats.
1936		K. Mackenzie Living Rough 183: These wharf rats abroad slink along dark alleys, preying on sailors or others when they think they have money.
1949		Monteleone Criminal Sl. (rev. edn).
1952		L. Hughes Laughing to Keep from Crying 161: He spoke the English of the wharf rats.
1958		H. Ellison Web of the City (1983) 37: He dressed like a wharf-rat.
1978		R. De Christoforo Grease 196: When the docks were being used it was probably a transport road [...] now it was left for wharf rats and greasers to tear up.

2. a woman who frequents waterfront areas where she can find sexual partners among sailors.

1967

S. Hugill Sailortown 5: Oversleeping, maybe, with some predatory and over-sexed wharf-rat.