Karalius, 20, came through the St Helens academy before moving to Cumbria ahead of the 2012 season.
Hawks Director of Rugby Darren Williams said: “We’re delighted to be able to announce the capture of Ben at a time when we are short of half back’s with Aaron Dobek the latest in a long list of casualties, he played against us back in February in the Northern Rail Cup and certainly impressed with his direction, illusiveness and organisation skills as well as his kicking game.
“I would like to thank Barry Richardson (chairman) and the Whitehaven club for reluctantly agreeing to release Ben after a week of negotiations.”
Mapals, 26, returns to the club for a second spell, and had been playing amateur rugby league with Methley, to help his return to match fitness.
Williams added: “Lee Mapals has had his problems off the field in the past but he’s trained with us and has shown the right attitude and application and is hungry for a second chance, Barry knows him well from his time with him at Keighley Cougars and if he reproduces his form of old we will certainly have a flair player on our books with renowned power and finishing pace.”
“I’m certain both players will make significant contributions in the season run in and both are in contention to make their debuts in Sunday’s home clash at South Leeds against Keighley Cougars.”