Oh, they are indeed a pain. sadly, same as before - you move carefully, leave time for reaction fire and have soldiers cover each other. The "shoot a rocket, ask questions later" policy is very helpful here.
If it is a real tough situation - terror missions with snakemen can end up having 8 of those things. Or taking a down snakemen terror ship can have 4-5. Worst case - show up, not even let your guys off the ship, and abandon mission. Still better than not going at all.
Eventually - heavy plasma + good reaction. Accept no substitue.