Jelly Fish of North Wales (2020)

Through the summer months jellyfish in north Wales are abundant in our waters. They drift through our sheltered bays, in the clear cool waters in search for food for a few months a year. They come in all shapes and sizes and some even pack a punch with their sting, but most are actually harmless. They travel in some cases thousands of miles, timing their arrival with algal blooms which they feed on, along the coast of Anglesey and the Celtic sea. You may have spotted blooms of jellyfish off the welsh coast, either if you have been sailing here or just out on your paddle board around the coast.

The jellyfish is a gentle intelligent creature, that much is miss understood I believe. A quiet predator of the seas, that roams purposely from coast to coast,  in search of temperate waters and its next feed.


Beaches for spotting jellyfish in north Wales

Some of the best beaches to find jellyfish are dotted on the map below. Click the image on the map and go through to the interactive version map to see. We will update this map over the summer. Most of the west coast beaches on Anglesey, are good venues to see jellyfish, the long sweeping bays seem to attract them into the shallows. The small bays we have highlighted on the map are perfect for snorkelling to spot them. Bigger beaches are better to see them washed up along the foreshore- such as Aberfraw or Newborough.


Best snorkelling coves for seeing jelly fish on Anglesey

I’ll keep this question to Anglesey or just off (Holy Island)  because north Wales can be to large a coastline to break down really. There are a few little coves and beaches that I like to snorkel in and around (where I spot jellyfish regularly) – Click on the image and you can get to the interactive map.


Jellyfish beach locations Anglesey and Holy island
Jellyfish beach locations Anglesey and Holy Island


Rhoscolyn Beach – West coast of Holy Island

Porth Daffrach – West coast of Holy Island

Porth Trecastell –West coast of Anglesey, near Rhoneigr

Porth Cwyfan – West coast of Anglesey, near Aberfraw

Rhosneigr – West coast of Anglesey

Trearddur Bay- West coast of Holyhead


Tips to avoid getting stung by jelly fish in north Wales

Well from me, when I’m spear fishing or snorkelling, I wear, wetsuit which is hooded, with booties and gloves. This keeps me from getting stung, I still get stung sometimes in late August, when the ones with long tentacles are floating about (they can brush against my face – but, its very rare (top tip grow a beard !). If your a open water swimmer, stick to long sweeping sandy bays instead of coves and you will find less jellyfish.


Jellyfish in north Wales (2020)

Well i’ll be honest, I’ve only had one snorkel session this year, so I’m a little out of the loop with what has been spotted in and around the bays.. (It’s July as I write this- I will update this as I go in two weeks after I have had a chance to snorkel, free dive and explore a bit more around the coast).


Are Jellyfish dead when washed up in north Wales ?

Not usually, they get driven to the shore and washed up due to environmental factors, and then unfortunately die. They travel in large blooms together sometimes in their thousands..


Can jellyfish survive on a beach ?

Not usually, the sun will desiccate they’re delicate rubbery bodies and sadly they will die. So many jellyfish get stranded along the shoreline, due to strong tidal currents, wind and storm swell, that they where not anticipating. It can happen with huge amounts of jelly fish on the anglesey coastline, on some years where blooms of jelly fish get caught off guard.


What is jellyfish in Welsh ?

For many years in Welsh jelly directly translated was ” Cont – y – mor” but recently its been changed to ” Sglenfren For” (sorry to disappoint all this who think its ” Wibbly- Wobbly” as some media outlets may have you believe!)


Top months to spot jelly fish in north Wales waters ?

Top month for seeing jellyfish in north Wales waters happens to be June – September from my own personal experience. Plankton blooms are high and water temperatures are favourable for them.


Whats the most popular type of jellyfish to see in Welsh waters ?

I’m sure the experts could wade in on this one, but I think its the compass jelly fish if we are talking sheer numbers of them. But I do see lots of other types equally, just not in the same numbers as I do these..


What creates an abundance of jelly fish in Welsh waters ?

Warm waters, plankton and food aka baitfish and marine life.


Giant jelly fish that wash up on the shores of north Wales 

So the largest type of jellyfish that gets into these waters are Barrel Jellyfish, see the image below. They can grow to astonishing sizes and live for many years. They often get seen more widely in the Celtic sea, than shallow waters around the coastline. Totally harmless they use the ocean currents to move in and around the coasts, feeding.

Barrel jellyfish- image by
Barrel jellyfish- image by



Atlantic jellyfish species 

So we have put together a bit of a comprehensive guide to most of the Atlantic jelly fish species you get to see in these latitudes, as with anything marine, we get surprise variants. We have made the listing quite comprehensive as you do occasionally get some of the more stranger varieties of jellyfish landing in our waters. Hope its useful for your jellyfish identification.


The different jellyfish you can find in north Wales waters 

We have put together a listing for you below for the various sorts of jellyfish you will find all across north Wales coastal waters.


  1. Mauve Stinger

Jelly Fish species known as Mauve Stinger can be seen in autumn and winter and normally they are found in large groups. During night time this jelly fish emits a bright glow when disturbed. They feed on other small jelly fish species as well as oceanic sea squirts. Its warty “bell’ which is full of stinging cells and the long tentacles together make a strong punch. These small amphibians hang out inside the ring formed by the tentacles and the hard outer shells ensure their protection.

How to identify?

Mauve Stinger is of mauve (bluish purple) color and it is covered with globe shaped hard shell which is covered by orange-brown warts. Thin tentacles hang down around the bell and these tentacles can be up to 3 meters long.

The Mauve Stinger jellyfish. Image :
The Mauve Stinger jellyfish. Image :


  1. Blue Jellyfish

This beautiful  Jellyfish can be seen along the UK coastline in summer and autumn. This jellyfish feeds on very small creatures known as plankton. They move inshore to eat the blooms of plankton. They drift along and catch the prey with the thick array of tentacles. It is advisable not to touch them since they sting. Lion’s Mane Jellyfish and Blue Jellyfish have similar shape but, Lion’s Mane is larger. Blue Jellyfish develops the blue-purple bell only when it matures. The young one appears colourless.

How to identify?

The matured Blue Jellyfish is identified with its dome-shaped, blue-purple bell and stinging tentacles that trail underneath. Younger ones are pale yellow in colour.


Blue jellyfish- Image
Blue jellyfish- Image


  1. Lion’s Mane Jellyfish

This jellyfish got its name from the stream of tentacles around its bell which reminds the mane of a lion. Lion’s Mane jellyfish feeds on fish and smaller jellyfish. Those who see this jellyfish should  not touch it since it gives a powerful sting. It’s tentacles are up to 3 meters long and are made of thick layers of stinging cells. They catch the prey using these tentacles. This North Wales jellyfish species are found off the UK costs during summer. The sting by this jellyfish is not only painful but nasty also. The injury may be severe and there can be swelling also.  Lion’s Mane jellyfish is a marine species. Even after getting detached from the jellyfish, the tentacles will sting so watch out!

How to identify?

This jellyfish is translucent brown to reddish in color and there will be hundreds of hair-like tentacles with length up to 3m. The oldest tentacles will be of dark red color. Thick, frilled oral arms in brown color can be found under the bell.

Lions mane jellyfish-
Lions mane jellyfish-


  1. Compass Jellyfish

The Compass Jellyfish got its name from the radial pattern of its bell which resembles a compass. There are brown markings on the bell. This jellyfish species are found along the UK shores in summer. They feed on small fish, other types of jellyfish and crustaceans. Those who find this jellyfish are advised not to touch it since it gives a sting. When it stings it leaves the tentacles on the skin of the victim and the tentacles continue to sting even after getting detached from the jellyfish. Size of this jellyfish will be normally 15 – 20 cm across. Compass Jellyfish is a marine species. Young fish can be seen swimming around the tentacles of Compass Jellyfish to protect them from predators.

How to identify?

Compass Jellyfish is of yellowish-white color. Brown markings can be seen on top of the bell and also around the fringe. “V” shapes can be seen radiating from a central point and the bell resembles a compass. Long thin tentacles are found around the fringe of the bell. Below the bell there will be a bunch of frilled oral arms.

Compass jellyfish - Image :
Compass jellyfish – Image :


  1. Barrel Jellyfish

This is the largest  jellyfish found in UK seas. Barrel jellyfish can be seen on the shore in early summer. This jellyfish can be seen throughout European coasts, especially the Mediterranean. They are also found around west and south coasts of British Isles, around the Welsh coast and elsewhere around UK. This large jellyfish can grow up to 1 meter across. However, those found in the British waters are half this size. Since they grow to the size of dustbin-lids, they are also known as Dustbin-lid Jellyfish. They feed on plankton and minute mid-water crustaceans. This jellyfish has 8 mouth arms that resemble cauliflower. This jellyfish has no tentacles to sting. Prolonged exposure can lead to allergic reaction and even the dead jellyfish can cause allergic reaction. Hence it is advisable not to touch it. This marine species is the most favorite food of leatherback turtle, which is the world’s largest sea turtle.

How to identify?

The normal color of Barrel Jellyfish is white to pale yellow. It is identified by its domed bell upper part and the bunch of 8 frilly tentacles below. There is a violate fringe around the bell. This frill contains sense organs.

Barrel jellyfish- image by
Barrel jellyfish- image by


  1. Moon Jelly

Being the most common jellyfish in the UK seas, the Moon Jelly is also known as Common Jellyfish. They are found in Irish waters during the period April – September. Moon Jelly is around 25 – 40 cm in diameter and has transparent body with short tentacles. On its back there are 4 pinky purple rings. This jellyfish doesn’t sting humans and they can be picked up from their back without getting stung. The 4 purple rings on the back are the reproductive organs that are located at the bottom of the stomach. Moon Jelly has delicate, short tentacles that hang down from the sides of its bell. They feed on plankton. They catch the prey using the layer of mucus over the bell. This marine species passes through two stages in its lifecycle – polyp and medusa. Polyp is a small stalk that gets attached to a rock and gets divided into buds. These buds break and grow as adults. The adult stage is known as medusa.

How to identify?

Moon Jelly is round as well as dome-shaped. It has a translucent body with 4 pinky purple rings on its back. This jellyfish floats just below the surface of water.

Moon Jelly Fish- Image by wikipedia
Moon Jelly Fish- Image by wikipedia


  1. By-the Wind Sailor

This species is closely related to jellyfish. They catch the wind and glide across the surface of water. This oval disk shaped marine species float on water and hangs its short tentacles down into water. They grow up to 10 cm by length. They are found throughout the year and sometimes they are found in large numbers on beaches. By-the Wind Sailor produces mild sting.

How to identify?

By-the Wind Sailor has oval shaped body which is deep blue in color. On the top of the body there is a vertical triangular vane.


By the wind jelly fish - pintarest
By the wind jelly fish – pintarest


  1. Portuguese Man-o-War

Though it appears like jellyfish it is not a jellyfish, but a colony of hydrozoans. The species is up to 10 inches long. The length of its tentacles is up to a few yards. This float can inflict a very painful, serious sting. When gales blow from Atlantic Ocean in summer and autumn, these species are washed up along the South Coast and occasionally in north Wales (I have seen them at Treaddur bay!). Because of its powerful sting this jellyfish like marine creature is considered very dangerous.

How to identify?

It is a large float that looks like a balloon and will be in pink, blue or purple color. It is about 30 cm long and 10 cm wide.


Portugese man-o-war- wikipedia
Portugese man-o-war- wikipedia


  1. Sea Gooseberry

This is not exactly a jellyfish but ctenophores. They are washed up on the shore when there is tide. They are very small and  harmless.

How to identify?

When underwater the transparent body of Sea Gooseberry refracts light into the different colors. It is about an inch long and has two branches of comb-like tentacles.


sea gooseberry jellyfish. Image Pinterest.
sea gooseberry jellyfish. Image Pinterest.


  1. String Jellyfish

This Jellyfish seen by those who dive off South West England, Ireland and Wales. This jellyfish has very long strings that are several meters long. This mid-water marine species is found near the coast. It can inflict sting on sensitive human skin. It is also known as Pearl-Chain Jellyfish.

How to identify?

It has dome shaped body in blue color with a lot of strings that are several meters long.


  1. Stalked Jellyfish

Stalked Jellyfish is found on rocks or algae in shallow waters near the coast. They are found on the shores of UK and Ireland. They are very small and are well camouflaged. Overnight they will appear and disappear.

How to identify?

Bell of Stalked Jellyfish is of maroon color. Within the bell there are 8 webbed arms At the end of each arm there will be up to 35 rounded tentacles. The distinct white spots on the bell are the stinging organs.

stalked jelly fish- image: pintarest
stalked jelly fish- image: pintarest


  1. Comb Jelly

Comb Jelly lives in mid-water. It feeds on smaller Comb Jelly as well as other jellyfish species. They consume the prey as a whole by wide opening the mouth. They are found on the western coast of the British Isles.

How to identify?

Comb Jelly has oval shaped body which is 15 – 18 cm long. The rows of cilia are visible inside the transparent body. When the Comb Jelly uses the cilia to move iridescent colors will appear.

Comb jelly fish-image
Comb jelly fish-image


13. Cannonball Jellyfish

Cannonball Jellyfish is found in Atlantic, Pacific and Gulf shores. Its bell is either jelly or milky. Body features a rim in brown shade. It has 16 forked oral arms and mucus-coated scapulets. This jellyfish feeds on fish eggs, red drum fish larvae, planktonic larvae and snails. It swims using its oral arms. When disturbed it will dive into deep water and releases mucus that contains toxin. In this way it drives away its predators. It can sense light, gravity and touch.

How to identify?

It has dome-shaped bell 7 – 10 inches by width and 5 inches by height. Rim of the bell is shaded in brown pigment.

Cannonball Jellyfish. Image flickr
Cannonball Jellyfish. Image flickr


To summarise, jellyfish of north Wales are abundant in our healthy seas and concur all across the coastline of Anglesey and north Wales, between June and September. You can spot them either long the foreshore washed up on large beaches like Rhosneigr or Newborough. There a good few species that pack a good sting so take caution with handling and assume that they do sting! They are inquisitive roamers of the ocean that are otherwise harmless and provide amazing viewing from aa snorkelers perspective !


Books on jellyfish and marine coastal waters of the UK.


Photo by KAL VISUALSon Unsplash


Tan Y Tro Nesaf  / Until the next time,



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