It is a common surname in German-speaking countries and can be found in Germany, Austria, and Switzerland. It means "prickle" or "thorn" in German, likely derived from a place name or a descriptive term for someone who lived near a thorny bush or had a prickly personality.
While there might be individuals with the surname "Stachel" in Poland, it is not a common surname there and is more likely to be found among people with German ancestry.