Revolting Rock Pools

If you like Horrible Histories you’ll love our monstrous marine life: it’s gory, gruesome and you only have to go down to the beach to see it happening right in front of your eyes.

First of all, check out my rock-pooling tips to help you find exciting things and to make sure you all survive the day unharmed. Next, grab a bucket and steel yourself for some stomach-churning surprises

Meet the top five contenders for the title of most revolting rock pool dweller:

 5      The Snakelocks Anemone

Snakelocks anemones in Cornish rock pool
Snakelocks anemones in a rock pool

The name is a great fit. This anemone’s spreading green or brown tentacles look like purple-headed snakes. From a distance they’re pretty, like flowers, but watch them closely and you’ll see that those tentacles aren’t just swaying in the current, they’re actively reaching out for flesh to consume.

Just like their relatives, the jellyfish, the anemone’s tentacles are covered in special stinging cells (called nematocysts) that fire out venom. Once it has paralysed its prey, the anemone grabs it and pulls it down to its mouth.

Some children are allergic to the venom, so don’t touch!

Watch what happens when a fly comes too close to a snakelocks anemone.

4      The Shanny

A shanny - also known as a common blenny
A shanny – also known as a common blenny

This cute-looking bug-eyed chap with his fat fishy kiss-me-quick lips wouldn’t hurt a fly, right? Well, flies may not be top of its list, but this is a determined little carnivore. The shanny loves nothing better than nibbling the legs off live barnacles.

3      The Green Shore Crab

Green Shore crab
Green Shore crab

If you’ve ever been crabbing, this is most likely the crab you’ve caught. It’s a robust and fearless creature, able to cope with extreme levels of salt and changes in temperature that would kill most other crabs.

It can sniff out a dead animal (or that piece of bacon you put in your crabbing net) from far away and it eats pretty much anything including other crabs. That’s right – it’s a shameless cannibal.

Baby shore crab in Cornish Rock Pool.
Baby shore crabs come in many colours and patterns.


2      The Starfish

Common starfish in the rockpools at Readymoney
Common starfish

OK, so starfish don’t look like they can do anything, but they don’t just sit around looking pretty. Nope, they are a fearsome predator, able to pop shells open and suck out the contents. They also have weird regenerative powers: if a starfish loses a leg or three, it simply re-grows them.

But what makes this number two revolting rock pool creature is how it eats. When a starfish finds something tasty it raises its body up over the victim and pushes its stomach out to engulf it, turning it to mulch with its powerful enzymes before sucking it all back in. Yum!

1      The Dog Whelk

Dog whelk next to its prey - a limpet
Dog whelk next to its prey – a limpet

I kid you not. This pretty, pointy shell, available in a variety of attractive colours completely deserves the number one spot. This is, beyond a shadow of a doubt the most revolting creature in our rock pools.

The dog whelk is equipped with a taste for flesh and a dastardly secret weapon – its radula. That’s a long, protruding device, with saw-like edges, so sharp it can drill a perfect neat hole through another animal’s shell.

If that wasn’t bad enough, it is also thought that the dog whelk then pumps stomach-type enzymes through the hole it has made. This gradually turns its victim to soup, which the dog-whelk sucks up through its radula, using it like a straw.

Next time you find shells washed up on the beach, look out for the tell-tale tiny hole that shows you how they met their fate.

Happy Rock Pooling!


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For everyone who loves Cornwall's rock pools. Information about great beaches, marine wildlife and conservation.

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