They are like the Spanish Nettle that burns and itches. My mother inlaw told me once when we were berry pickin to pee onit !!! Ammonia, huh? Well, I put clear polish onit. Smothered and it wears off and you can't see it. Good Luck,
Blessings,
Ruth (ps, man-o-war stings are like that. you can use ammonia on it and we kept it in our first aid kit on the boat)