Tekrapod’s Guide to: Jellyfish found around the British and Irish coasts and what to do when you get stung by one.

Open water swimmers are more than familiar with the jellyfish. Despite their beauty their stings can be a real pain. Most of the time they leave behind a mild sting, similar to a nettle’s. However, there are a few jellyfish that can leave behind a nastier sting and may require medical attention. So we did the research and compiled a list of the all the jellyfish you’re likely to encounter on your swimming adventures and what to do if you are unlucky enough to get stung.

Common/Moon Jellyfish (aurelia aurita)

Distinguishing features: This jellyfish is easily recognised by its four horseshoe-shaped gonads on the top of its bell. It’s mostly transparent, except for its pale pink to orange tentacles and gonads.

Where it’s spotted:  It’s found in all UK and Irish waters, particularly in marinas, estuaries and bays. It’s most commonly seen from mid spring through to mid summer.

Severity of sting:Their sting is extremely mild and nothing to worry about.

Compass jellyfish (chrysaora hysoscella)

Distinguishing features:These jellyfish are characterised by V-shaped brown stripes that radiate out from the centre of the bell, like the points of a compass. They are up to 30cm in size and have 24 long thin tentacles and four frilled “arms” hanging underneath.

Where it’s spotted:The compass jellyfish are found mainly in the southern half of the UK during the summer months. It’s found generally between July and September in Irish waters.

Severity of sting:They’re not dangerous, but their sting can be quite painful.

Blue jellyfish (cyanea lamarckii)

Distinguishing features:This jellyfish is typically a bright blue/purple colour but there are also brown morphs. It has a scalloped edge and long, fine tentacle trailing underneath.

Where it’s spotted:It is common in the South West and Wales during the late spring to summer months, but can also be seen along the North Sea coastline. It’s less common in Irish waters.

Severity of sting:It has quite a painful sting.

Mauve Stinger (pelagia noctiluca)

Distinguishing features:It is relatively small (10cm) and is characterised by a more conical shape covered in pink or mauve warts. Four long frilled arms hang underneath.

Where it’s spotted:This jellyfish is common in the Mediterranean during the summer. It is rare in the UK and only found along the south coast in warm summers. In Irish waters it’s mostly found during the autumn and winter months.

Severity of sting:This jellyfish has a nasty sting.

Barrel Jellyfish (rhizostoma octopus)

Distinguishing features:This jellyfish has a very distinctive solid, rubbery bell up to one metre in diameter. Its colour varies from pale pink, cream or brown fringed with purple markings around the edge.It doesn’t have tentacles, they’re more like thick frilled arms.

Where it’s spotted:Barrel jellyfish are less common, being found mainly along the coastlines of the South West, Ireland, Wales and Western Scotland, either in more open water or washed up on beaches in the summer and autumn months. It’s believed that they live year round.

Severity of sting:Although they can be very large, this jellyfish is harmless and has only a very mild sting.

By-the-wind-sailor (velella velella)

Distinguishing features:While not a true jellyfish they are a close relative. These beautiful creatures are blue in colour and shaped like an oval disk with a small sail. This ‘sail’ allows them to catch the wind and glides them across the surface of the water.

Where it’s spotted:The velella can occur in vast swarms and if there are strong westerly and south-westerly winds blowing in from the Atlantic Ocean in the late summer and autumn months. Huge numbers can be found stranded along the South West of England and Welsh coastlines, although this is rare. In Irish waters they can arrive at any time of the year.

Severity of sting:They are harmless.

Lion’s Mane (cyanea capillata)

Distinguishing features:The scalloped-edged bell is reddish-brown in colour and can range in size from 30cm up to two metres in diameter. A mass of very fine tentacles trail for up to 10-20 metres.

Fun fact: The lion’s mane is a relative of the blue jellyfish.

Where it’s spotted: It prefers colder waters, so it is found mainly from North Wales, right up to the north of Scotland and beyond. There have been lots of reported sightings of these along the east coast of Ireland.

Severity of sting:These guys have a nasty sting that can result in blistering and anaphylactic shock. So if you are stung it’s wise to seek medical assistance immediately and notify a lifeguard or local authorities so other’s aren’t put in harms way too!

Portuguese Man O’War (physalia physalis)

Distinguishing features:The characteristic purple-blue oval-shaped float with “tentacles” hanging for up to tens of metres underneath is familiar to many people.

Fun fact:It is not a jellyfish; instead a colony of hydrozoans. It lives in the open ocean floating at the surface.

Where it’s spotted:If gales blow in from the Atlantic Ocean in the late summer and autumn, several may get washed up along the South Coast of England , although this does not happen every year.

Severity of sting: The Man O’War can leave behind a really severe sting. So, once again it is advised to seek medical assistance immediately to be on the safe-side and again notify your lifeguard or local authorities to prevent it happening to other swimmers. It should be noted that even when washed ashore they can retain their sting. So it’s best to steer clear whether they’re in or out of the water.

Important!! If you spot a Portuguese Man O’ War or Lion’s Mane in the water a lifeguard should be notified immediately !!!

Now for the most important part! What to do if you do get stung.

  1. Wash the affected area with seawater not fresh water, vineagar, alcohol or urine.
  2. Don’t rub the affected area as this can result in further venom release.
  3. Carefully try to remove any tentacles or stingers left behind with tweezers or a gloved hand.
  4. A heat pad may help relieve the pain.
  5. Painkillers such as paracetamol or ibuprofen could also help
  6. If symptoms should become more severe, or a sensitive part of the body has been stung, you should immediately seek medical help.
  7. If you have been unfortunate enough to have been stung by what you think is a Portuguese Man O’ War or a Lion’s Mane you should seek medical assistance immediately!!

Can a jellyfish sting when it’s dead?

We discovered this question during our research of the subject and were surprised with the answer. Yes, they can! Dead or alive if their tentacles are wet, jellyfish can still sting. So even if you see a jellyfish stranded on the beach, it’s best to steer clear and stop your curious dog and children from having a sniff.


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Size guide

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