A bunch of us got stung by younger jellyfish (2-3 ft long) either during the swim warmup or while racing IMMD in 2017. Maryland had unusually warm climate throughout the year -especially earlier in the year which also caused all of the cherry blossom trees to bloom one month too early. I got stung in the face during the race. It stings but it won’t stop your swim. The pain fades. It is not a show stopper. The sting popped up sporadically throughout the race but honestly there are so many other things you worry about. You will endure other pains that will make you forget about it. After experiencing it, It wouldn’t even be a concern on my radar pre-race. If it happens, it would just make for a fun dramatic IM story later.