If Silver Sol makes it move, then you know it is effective. But if you keep spraying it, it could move into deeper tissue. I would probably take the silver sol or equivalent ingredients internally, hoping the dang worm would hop off my body to get away from it. You might have to endure the thing moving around looking for a safe place to suck blood before he decides to abandon the host, however. And that could be really creepy. Is there anything you could take to paralyze the darn thing first, so he couldn't squirm when you saturated your bloodstream with the stuff he hates?