If you plan on spending time on any tropical beaches this summer, you might see a jellyfish or two on the sand. Jellyfish can lurk in the ocean water as well, creeping up on you where you can’t see them. Jellyfish stings can be seriously painful; when they strike, their tentacles inject venom into the skin from thousands of microscopic barbed stingers. If you are stung, exit the water immediately and seek medical attention. Remove the barbs with a credit card or other plastic object and rinse the affected area as soon as you can. You can use ocean water to rinse, or vinegar if you have some available. Portuguese man o' wars, though different from jellyfish, pose a similar threat. Watch out for them on the sand.