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A guide to jellyfish in Cornwall

compass jellyfish

Nothing strikes fear into the heart of a sea swimmer quite like the prospect of sharing the water with a jellyfish. But ocean goers needn’t be afraid — most of those found in Cornish waters are harmless, with only a few of species giving a nettle-like sting. Read our guide to jellyfish in Cornwall and don’t let jellies get in the way of your enjoyment of the sea.

Jellyfish species

There are thousands of species of jellyfish in the world but only a few are commonly spotted in Cornwall, including the moon jellyfish, the compass jellyfish and the blue jellyfish. Jellies tend to remain offshore but if they do float towards land, they’re often easy to spot, especially in clear water. The best thing you can do is to get to know your species of jellyfish in Cornwall so you know which ones to avoid should you see bobbing about in the water.

Moon jellyfish
The UK’s most common jellyfish, often seen in large numbers during the summer months, there’s no need to avoid this one in the water — the Moon Jellyfish is harmless to humans. About the size of a dinner plate, it is recognisable for its four distinct purple-pink circles visible through the bell and short tentacles.

Compass jellyfish

compass jellyfish

This regular visitor to Cornwall’s shores is so named because of the brown markings on top of its translucent bell, reminiscent of a compass. They have frilled oral arms below the bell and long thin marginal tentacles around the fringe of the bell which can give a mostly mild sting, like brushing against some nettles, so it’s best to give it a wide berth when out in the water.

Blue jellyfish
This beautiful jellyfish is often seen around the UK coastline in summer and are attracted inshore by plankton blooms that provide a plentiful supply of food. It’s dome-shaped bell can vary from pale yellow to purple in colour, and its tentacles trailing underneath can sting. The paler (younger) ones are easily confused with the larger lion’s mane jellyfish.

Barrel jellyfish
With a large translucent, mushroom-shaped bell and a bunch of frilly tentacles below, these large jellyfish swarm in warmer coastal waters in late spring and often wash up on Cornwall’s beaches in May or June. Their sting is not normally harmful to humans, though if you find one on the beach it’s best not to handle it as they can still sting when dead!

Lion’s Mane Jellyfish
With a thick ‘mane’ of hair-like tentacles, the lion’s mane jellyfish is the largest jellyfish in the world. It’s very rare in Cornwall but can very occasionally be seen in the waters around the coastline. Needless to say, it can give a nasty sting, even when found washed up on the shore, so it’s best avoided.

Treating a sting

In the majority of cases, getting stung by a jellyfish in Cornwall isn’t painful but can cause a rash. If this happens, it’s best to rinse the affected area with sea water (not fresh water), remove any tentacles with a pair of tweezers and soak in warm water — as hot as you can handle — as soon as you can. If the symptoms persist or are more severe, it’s probably best to seek medical help. Swimming in wetsuits can provide protection if you’re feeling anxious about them, but, as this guide shows, there’s really no need to be fearful — stings are rarely a cause for concern, with the benefits of swimming in Cornish waters far outweighing any threat of jellyfish stings!