All Jellyfish do not sting.
Many species of jellyfish are harmless and do not sting humans or other prey. But most people, when encountering a jellyfish in the ocean, have an immediate knee-jerk reaction, regardless of whether it is of a kind that will try to sting or not.
Southeastern Atlantic Species
In the Atlantic Ocean for example, off the coast of South Carolina, the Cannonball Jelly and the Mushroom Jelly are harmless to humans. Then comes the Southern Moon Jelly, the most common type of jellyfish in these waters. If humans brush up against one, they will not necessarily get stung, per se, but contact with their slightly venomous tentacles can produce mild, localized pain. The same goes for the Lion’s Mane.
But if the species of jellyfish in the Atlantic waters is a Sea Nettle, Sea Wasp or Portuguese Man-of-War, then being stung is very much a dangerous possibility. The sting of the Man-of-War, in particular, can produce all sorts of sideline symptoms including vomiting, fever and even hysteria. Serious stings with inflammation will require medical care. But on the home remedy front, all sorts of food and liquid substances have been found to alleviate the pain. Everything from meat tenderizer to bicarbonate of soda.
New Monterey Breed
Perhaps scariest of all is the idea that not all species of jellyfish have yet to be identified, and that as exploration into the deepest reaches of the ocean continues, even more powerful stings could be discovered. Several years ago, scientists in Monterey, CA came across a new kind of jellyfish that they dubbed granrojo, or “Big Red.” Instead of tentacles, it has between four and seven legs protruding from its body. This jellyfish is a predator, but does not necessarily have the ability to sting humans. During the summer of 2010, black sea nettle jellyfish suddenly started appearing without warning in the waters of San Diego Bay. They are a stinging species, so locals were told to be mindful.
South Carolina Department of Natural Resources – Jellyfish, Retrieved December 2, 2010 from http://www.dnr.sc.gov/marine/pub/seascience/jellyfi.html
National Geographic – “New Jellyfish Species Found”, May 5, 2003, Retrieved December 2, 2010 from http://news.nationalgeographic.com/news/2003/05/0505_030505_tvnewjellyfish.html
USA Today – “Rare Dark Jellyfish Species Showing Up in San Diego Bay”, July 14, 2010, Retrieved December 2, 2010 from http://www.usatoday.com/tech/science/discoveries/2010-07-14-rare-jellyfish_N.htm