At a distance it appears harmless, because it is rooted in the ground - however if you step closer to it, then it will burrow out and snap at you. It can't move, so it can't be lured anywhere. Put one block between yourp player character and the Warmworm in the right position, then it can render it's attacks useless, while you can kill or tame it without ruffle... Warmworms have a special attack spewing a lava fountain, which inflicts fire damage, and they can also use an ordinary bite attack. Tamed Warmworms might prefer to eat Bread, Soup or Sandwich.