Jellyfish on the Spanish coast: what stings, when they arrive, and what to do

Jellyfish are the hazard most likely to interrupt a Spanish beach day, and the one surrounded by the most confident bad advice. What follows is general information about a common situation. It is not medical advice: if a sting is severe or you are worried, go to the lifeguard post and then to a doctor.

The ones that cause trouble

Only a handful of species account for most incidents on this coast, and they are not equally unpleasant.

• Pelagia noctiluca, the mauve stinger — small, purple-brown, and the cause of most stings in the western Mediterranean. It arrives in numbers rather than alone.
• Rhizostoma pulmo, the barrel jellyfish — large, pale, with a violet fringe. Its sting is mild, and its size is more alarming than its effect.
• Cotylorhiza tuberculata, the fried egg jellyfish — unmistakable and largely harmless to people.
• Velella velella, the by-the-wind sailor — small blue discs that wash up in drifts. Not a danger to swimmers.
• Physalia physalis, the Portuguese man o' war — not a true jellyfish but a colonial siphonophore, mainly an Atlantic visitor and only occasionally in the Mediterranean. Its sting is severe. Treat it as a medical matter, not an inconvenience.

The wind decides, not the season

Jellyfish have almost no power to swim against a current. Where they end up is decided by currents and by the wind, which means a beach can be clear for a fortnight and unusable the next morning without anything about the weather changing for the worse.

A steady onshore wind is the thing to watch. It pushes whatever is drifting offshore towards the sand. An offshore wind does the opposite, which is why the same stretch of coast can be crowded with jellyfish on one day of a settled sunny week and completely clear on another.

Numbers are generally higher in the warmer months, but the day-to-day answer is a local one. The lifeguard service knows, and on many beaches a purple flag is flown alongside the usual colour to signal hazardous marine life.

Why some years are worse

Researchers looking at long-term patterns point to several contributing factors: warmer water, dry years in which reduced river outflow weakens the low-salinity barrier that normally keeps jellyfish offshore, and reduced numbers of the fish and turtles that eat them. These are contributing explanations for a complicated system rather than a settled account, and none of them help you on a Tuesday. The wind still does.

If you are stung

The goal of first aid is to stop the stinging cells that are still on your skin from firing. Most of the traditional remedies make that worse.

• Leave the water calmly and tell a lifeguard. They deal with this daily and will have what is needed.
• Do not rub the area — not with sand, not with a towel, not with your hand. Friction fires the remaining stinging cells.
• Rinse with seawater, never with fresh water. Fresh water triggers the cells that have not yet fired, which turns one sting into many.
• Remove any visible tentacle fragments with tweezers or the edge of a card, not with bare fingers.
• Apply cold for about fifteen minutes to relieve the pain — an ice pack in a sealed bag or wrapped in cloth, so that no melt water reaches the skin.
• Watch the area over the following hours and days. Some stings blister or mark, and some react later.

Two things not to do

Urine does not help. It is mostly water of an unhelpful concentration, and it does exactly what rinsing with fresh water does. This is the single most persistent piece of beach folklore and it makes stings worse.

Do not improvise with vinegar, alcohol or ammonia either. Vinegar genuinely helps against some species and genuinely worsens the sting from others, so the right answer depends on what stung you — which is precisely the thing you cannot determine while it hurts. Ask the lifeguard rather than guessing.

When to seek medical help

Go beyond first aid, without waiting, if any of the following applies:

• Difficulty breathing, chest pain, dizziness, nausea or cramps
• A sting over a large area of the body
• A sting to the face, eyes or mouth
• The person stung is a young child or elderly
• Any known allergy, or any reaction spreading beyond the sting itself
• A suspected Portuguese man o' war

Things worth knowing beforehand

A dead jellyfish on the sand still stings, and so do detached tentacle fragments floating in the shallows — which is why a beach can sting swimmers on a day when there is nothing visible in the water. Shuffling through a drift of washed-up jellyfish barefoot is a bad idea for the same reason.

If you are going somewhere with a history of them, a cheap pair of water shoes and the knowledge that the purple flag exists will get you most of the way. And when the flag is up, the water is closed for a reason that has nothing to do with the waves.