To tame them u must go to the big tree part of the bog the one with glowing flowers they are on the trees branches there a bit hard to find i took 25 mins to find 1 to tame one you jump around under them until they grab you one once they get a hold of you make sure you have 200 bloodbags for low lvl or 1000 for high lvl just stay there and do nothing you'll start taming them be wary of swarms they are the worst when taming a stalker

More Bloodstalker Taming & KO Tips