UK tourists visiting Spain issued urgent warning over ‘jellyfish invasion' (2025)

The Portuguese Man of War jellyfish has been spotted on Spanish beaches

UK tourists visiting Spain have been issued an urgent warning as popular Spanish beaches are experiencing "jellyfish invasions" after the dangerous Man of War and more harmless sail jellyfish have been spotted in numbers.

Rising temperatures and environmental disruptions have led to a surge in the jellyfish populations, prompting swimming bans and medical emergencies along the Spanish coastline, reports Spanish news site Majorca Daily Bulletin.

The site reports that over the past week large numbers of jellyfish have been a number of popular beaches in Mallorca. However, it appears jellyfish are now swarming the coast across the Balearics.

Hundreds of sail jellyfish, Velella Velella, covered the beach of s'Arsenal in Mallorca over the weekend after heavy wind and waves. This mass stranding has been explained by being particularly vulnerable to changes in wind and currents.

Despite their appearance and sting, the velella are actually completely harmless to humans, although it is recommended to avoid direct contact with open wounds as that can cause a mild allergic reaction.

But in contrast to the sail jellyfish which are fairly harmless, the stinging, venom-filled nematocysts in the tentacles of the Portuguese man of war jelly can paralyze small fish and other prey.

Tourists and Spanish residents are being warned that detached tentacles and dead specimens washed up on the beach can sting just as painfully as those of the live organism in the water.

Stings by a Man o' War usually cause severe pain to humans, lasting one to three hours. Symptoms include red, whip-like welts appear on the skin that last two or three days after the sting.

In some cases, the venom may cause symptoms that mimic an allergic reaction, including swelling of the larynx, airway blockage, cardiac distress and shortness of breath. Other symptoms may include fever, circulatory shock and in extreme cases, even death, although this is extremely rare.

Medical attention for those exposed to large numbers of tentacles may become necessary to relieve pain or open airways if the pain becomes excruciating or lasts for more than three hours, or if breathing becomes difficult.

The Portuguese Man of War (Physalia), are not technically jellyfish but rather colonial organisms, can be particularly harmful to individuals with weakened immune systems.

Last summer, an estimated 7,000 swimmers sought medical treatment for jellyfish stings along Spain’s beaches, a 40 percent rise from the previous year, reports the Majorca Daily Bulletin.

The sharp rise in jellyfish populations can largely be attributed to climate change. Researchers from the Institute of Marine Sciences in Barcelona highlight the role of warming sea temperatures in facilitating the rapid reproduction of jellyfish. These conditions allow jellyfish to thrive, particularly in coastal areas that attract large numbers of swimmers.

In addition to warming waters, intensive fishing practices and the rapid urbanization of Spain’s coastlines have further contributed to the growing jellyfish problem. Coastal developments, such as resorts and hotels, disrupt marine ecosystems and decrease the number of natural predators, such as certain fish species, which would typically keep jellyfish populations in check.