Yes they pack a powerful sting, I wouldn't touch with your bare hand. They are very hard to get rid of. You can find several post on here if you do a search. To rid them is a battle and depending on how many you have the methods can very, but get rid of them as asap before they spread to the whole tank. I fought mine for at least two years. You can try covering them with a kalk paste if it is only a small area. If all possible remove the rock they are on from the tank and battle them outside of the tank. This will help in keeping them from spreading. You could also try removing the rock and use a hard bristle brush to scrub them off the rock. I have heard some poeple use tweezers to remove them from the rock, but that has to be some work. You have to be sure to remove all trace of them including the runners or they will grow back. I finally had to remove the rock from the tank and placed it in RO water in a covered trash can for about a month. After that I scrubbed the rock and blasted it with a hose rinsed it and placed it in a covered trash can with salt water for another month. Unfortunately this kills the whole rock, but it was they only way I could win the war. Good luck.