Green’s Dictionary of Slang

(Irish) a cockroach or a beetle.

1939		‘Flann O’Brien’ At Swim-Two-Birds 286: The attic was infested by clocks.
1994		(con. 1920s) K.C. Kearns Dublin Tenement Life 185: And clocks running around. Did you ever see a clock? Big black, hard things and little legs. Me mother’d be killing them with hammers.
1998		T.P. Dolan Dict. Hiberno-Eng. 661/1: clock n. black beetle.