Portuguese Man o'War creatures regularly make appearances on Spanish beaches especially on the Mediterranean resorts.
The man o'war – not strictly a jellyfish but a floating colony of microscopic hydrozoans – has tentacles that can reach 30 yards long and are barbed with a sting that typically cause painful welts lasting up to three days.
In some cases the sting can cause an allergic reaction and in rare cases, heart failure.
Even when washed up on the sand the stings still contain venom.
Rule No. 1: Don't touch it
Man-of-war fish have stinging cells that are still active and capable of stinging even after the creature is dead and washed up on shore. So don't touch it.
Rule No 2: Listen to lifeguards
If the red flag is raised then don't go into the water. If you break that rule you may face a fine or even be stung by one of the creatures lifeguards are trying to protect you from.
If you are in the water then you may be stung without even seeing the culprit. The Man-of-war looks like a floating blue plastic bag but they have practically invisible tentacles that typically extend over 2.4 meters (8ft) under the surface of the water and sometimes stretch to 10 meters.
Rule No. 3: Get help if you are stung
If you are stung then leave the water immediately and look for a lifeguard. If there are no lifeguards on the beach, wash the wound with salt water and remove any tentacles stuck to the skin by dousing the site with sea water.
Never use fresh water as that can actually cause the stinging cells, or cnidae, left on your skin to discharge, which could make the sting worse..
Don't touch the tentacles with your bare hands, and don't scrape them off your skin with objects like a credit card or razor, because that could increase pressure around the sting and make it worse.
Some experts suggest cooling the area down by applying ice for around five to ten minutes. You can also try wetting the wound with vinegar or baking soda dissolved in water.
Protect the area by using an antiseptic to avoid infections.
If the pain continues, make sure you consult a doctor.
Rule No. 4: Don't pee on it
Professor Josep Maria Gili from Barcelona's Institute of Marine Sciences warns against the common myth that urinating on a jellyfish sting can help ease the pain.
“That is absolutely false,” he told The Local.
“It could be effective for some fish bites but never for jellyfish.”
In fact, it might actually make the stings worse.
Rule No. 5: Seek medical attention
If you get stung by a man-of-war and you have trouble breathing, this could be a result of severe envenomation, and you'll need to see a medical professional immediately.
Extremely painful stings also require medical attention, as do stings that make you feel dizzy or disoriented.