Club captain March switched to hooker in the second half of this year, as the Hawks failed to avoid relegation, while Grimshaw turned down offers elsewhere to stay.
Director of rugby Darren Williams said: “We’re thrilled that David has decided to go around one more time, he was considering retirement but when switched to hooker for the second half of the season had a new lease of life and rolled back the years with some inspirational displays.
“His commitment to this club can never be doubted having played the last Championship game with a broken thumb, he’s our leader and our captain and someone you want in the trenches with you in the heat of battle.
“Danny had offers from two Championship clubs and a Championship 1 offer on the table but he has decided to stay and his loyalty is a real credit to himself and the club, he’s had a frustrating couple of years but hopes his luck will change and to keep a playmaker of his ability following relegation is a real coup.”
Mapals scored 11 tries in 16 appearances in 2013.