Posted by Ruby Tzimeas on June 23, 2006

Q: I live in Hawaii near a shoreline that is full of offshore freshwater springs. I and a few others have been stung by something in the ocean water that we can't see. It seems to get under the looser parts of our bathing suits and leaves swollen, red, itchy welts that last far longer than any insect bite. One person was told by a dermatologist that they are hydra stings. This is definitely taking place in the water, not on the shore. What do you think? Mahalo!

State: Hawaii

A: I've had some similar experiences myself. When I had my "stings" I remembered that I had been swimming among lots and lots of small jellyfish. Seems they were able to sting on contact but were not strong enough for me to note immediately. Later, my skin reacted to these with small swollen areas similar to what you experienced. Hydra are closely related to jellyfish and sting in the same manner so either there are some jellyfish in your area or the hydra story is correct (although hydra attach to substrate, in my experience and are not free-floaters). If I had to choose, I'd choos the jellyfish as the culprit. Keep in mind that some jellyfish are very difficult to see so you may have overlooked them. Jellyfish can be very numerous in an area at one time and totally absent the next so I hope you'll be able to swim in your area most of the year. My very best to you. Aloha.

John Wiessinger ( June 25, 2006)