Serine protease that functions in the melanization-mediated immune response (PubMed:16935219, PubMed:26926112). Preferentially, cleaves substrates with an arginine at the P1 site (PubMed:26926112). May be involved in the activation of the prophenoloxidase cascade upstream of CLIPB9; does not cleave prophenoloxidase (PubMed:26926112). The clip domain consists of 35-55 residues which are 'knitted' together usually by 3 conserved disulfide bonds forming a clip-like compact structure. Proteolytic cleavage is necessary for activation. RNAi-mediated knockdown in female does not affect lifespan and basal melanization (PubMed:26926112). Simultaneous RNAi-mediated knockdown of SRPN2 and CLIPB8 in female, reduces the spontaneous melanization and the lifespan shortening occurring in SRPN2 RNAi-mediated knockdown (PubMed:26926112). RNAi-mediated knockdown severely reduces the melanization of injected Sephadex beads (PubMed:26926112). Belongs to the peptidase S1 family. CLIP subfamily. Interacts with serine peptidase inhibitor SRPN2 in vitro; however, SRPN2 does not inhibit CLIPB8 activity suggesting that CLIPB8 may not be a physiological target of SRPN2 in vivo.