Green’s Dictionary of Slang

a street thief who specializes in snatching (drunken) men’s jewellery; thus bug–hunting, robbing or cheating drunks, esp. after dark.

1851		‘Adventures of Mr and Mrs Sandboys’ in Bells New Wkly Messenger 9 Mar. 6/2: The lady and gentleman racket, or stealing cocks and hens from the markets; and bug-hunting, or looking out for drunken men [i.e. to rob].
1856		H. Mayhew Great World of London 46: Those who hocus or plunder persons by stupefying; as [...] ‘drummers,’ who drug liquor; and ‘bug-hunters,’ who plunder drunken men.
1861		(con. 1840s–50s) H. Mayhew London Labour and London Poor IV 282/1: They loiter about the streets and public-houses to steal from drunken persons, and are called ‘Bug-hunters’ and ‘mutchers’.
1869		J. Greenwood Seven Curses of London 88: Midnight prowlers who rob drunken men – bug hunters.
1873		Sl. Dict.
1882		Sydney Sl. Dict. 10/2: The padding ken of Sally Hicks, who’s got a new moniker, which is Lushing Loo, is full of bug-hunters, and shallow coves, and fellows on the high fly. The two crocuses are gadding the pad to fence their gammy stuff.
1888		D.V. Lucas Aus. and Homeward 334: Some of their slang may be interesting [...] midnight prowlers who rob drunken men, bug hunters.
1895		Crowe Aus. Sl. Dict. 12: Bug Hunter, a low thief who robs drunken men.
1900–10		Stephens & O’Brien Materials for a Dict. of Aus. Sl. [unpub. ms.] 30: BUG HUNTING: is searching drunken men who are asleep in parks and elsewhere. BUG HUNTERS [...] a pickpocket who makes a speciality of snatching away breast pins, studs, etc.
1935		R.T. Hopkins Life and Death at the Old Bailey 63: The following crook’s words and phrases date from the days of the old Old Bailey: [...] plunderers of drunken men – bug-hunters.