When you think of fatally poisonous animals, surely large snakes and black spiders with bad tattoos flash through your mind. However, did you know that the box jellyfish, Chironex fleckeri, is in the top 10 of earth’s most venomous creatures? Its venom can kill a person within 15 minutes. A swarm of them almost stopped pro swimmer Diana Nyad from completing her swim from Florida to Cuba. Even if you don’t swim near the Indo-Pacific waters, be aware of balloon-like objects in the water around you when going to the beach this summer.

Avoiding jellyfish and protecting yourself from being stung

You can reduce your risk of getting stung by jellyfish if you swim at beaches manned by lifeguards. Lifeguards often raise a purple flag or verbally announce warnings when jellyfish are present in the immediate surrounding waters.

Most jellyfish, except for the box jellyfish, are immobile and simply float in the sea carried by waves and the wind. Out of abundance of precaution, don’t swim if the wind is blowing from the sea toward the shore since there’s a higher likelihood that jellyfish are being carried toward the shore.

While swimming, stay a few yards away from balloon-like transparent objects near the surface of the water. Jellyfish tentacles, which house their stinger cells (nematocysts), are long and can extend many feet away from their main balloon-like body.

Full-body swimsuits can protect you from most jellyfish stings. However, Portuguese man o’war’s stingers can penetrate rubber suits. Special topical sprays can prevent nematocysts from firing when making contact with your skin — Diana Nyad used one of these to successfully protect her bare skin from box jellyfish during her Florida-Cuba swim.

What to do if you’ve been stung

Jellyfish stings leave a painful, burning, stinging sensation. Don’t follow your initial reaction to run cold freshwater over the wound. Jellyfish are native to the sea, and their nematocysts are comfortable in seawater. Any nematocysts on your skin which haven’t fired their stingers might fire them if bombarded with shocking, unfamiliar freshwater. Wash the wound with seawater instead, then flush and soak it profusely with vinegar, isopropyl alcohol, or other disinfecting agent for 10 minutes.

After killing the nematocysts with disinfectant, remove any jellyfish tentacles still on your skin. Don’t try to remove them with bare hands before disinfecting since any unfired nematocysts will simply sting your hands – but you’re best off using tweezers.

Soak the wound in hot water for half an hour to relieve the pain. You can also use cold packs, papaya fruit paste, and citrus juice.

If you’re allergic to jellyfish venom, have epinephrine shots and antihistamines available. Get emergency medical help immediately if you start experiencing difficulty breathing, extreme inflammation, or other signs of severe allergic reaction.

Don’t let jellyfish ruin your summertime beach fun. Avoid getting painful stings by staying away from balloon-like objects in the water and not swimming when you see the lifeguard’s purple flags or when you see that the wind blowing from sea to shore. If you do get stung, treat the wound with seawater and vinegar, not tap water!