Crawlers are really squishy. The problem with having a hard counter to something is that once you have it, there's no threat any more. I get that you're having a hard time with crawlers but there are plenty of ways to deal with them as is, without adding an "I win!" button.
First, most places with crawlers have environmental clues to let you know you're about to walk into danger.
Second, crawlers are predictable, so you can make a bunch of noise then start chucking incendiaries like you're the worst Santa ever and you'll catch them in the fields of fire - then you can pick them off easily.
Third, you can carry antidotes so when they pop up and tag you, you can avoid their stun - once they don't have stealth or a stun potential, they're really not very dangerous at all.
Fourth, of course, you can try to boost your Perception and/or Detection so that you can see them before they hit you.
