More than a thousand bathers sought treatment from first aiders along the Malaga coast of southern Spain over the weekend as coastguards sought to contain the invasion. Several beaches were red flagged – prohibiting swimmers from entering the water.
This year scientists have detected an unusually large plague of the Pelagia noctiluca, commonly known as the "mauve stinger", small purplish bell shaped creatures which deliver painful stings through hairlike tentacles that can reach three metres in length.
Bathers have reported painful nettle-like burns that take up to three days to clear and can provoke asthma and allergic reactions. In extreme cases the stings have been known to cause heart failure.
The jellyfish have proliferated after a winter that saw a lack of rain in the Mediterranean region and higher than normal temperatures.
Experts also blame overfishing in the region which has left the jellyfish without natural predators such as turtles, tuna and swordfish.
"A dry winter, a warm spring, and particular tidal currents plus the elimination of predators to eat them, have all compounded the problem," said Juan Jesus Martin, a marine biologist with oceanographic agency Aula del Mar.
Maritime agencies along the coast have been tasked with collecting swarms of the gelatinous creatures as currents sweep them towards beaches. In Malaga province, some 1,700lb of jellyfish were caught in baskets on one day and brought on land to be destroyed.
Posters plastered at the entrance to beaches across Spain warn of the dangers and the best way to treat stings, which is to bathe the affected area with salt and not fresh water.
People are advised to seek immediate treatment from first aiders stationed on every municipal beach area.