Do Marine Hermit Crabs Kill Snails For Their Shells?

hermit inside a live conch

From everything I’ve read about hermit crabs, the consensus is that they don’t harm snails. They wait to find an empty shell and then move in.

When beach-combing, I see far more hermit crabs inside shells than actual live conchs and whelks, or the snails which made the shell. I find that odd, since there is quite a good ecosystem out on the mud flats. Very few people mess with beach nature out there. Visitors prefer the ocean beaches, and even the boaters either fish or sit and enjoy the tranquility found on a little sandy beach away from crowds.

It’s curious that I don’t see many more living snails. Then, I came upon this unusual scene.

Hermit Crabs and the Crown Conch

We pulled up to a little island the other day and as soon as I stepped out of the boat I saw this cluster of hermit crabs. A cluster of hermits in various shells is a regular sight, but one of the shells had a conch inside. And when I looked closer, I saw something I’d never seen before.

gathering of hermit crabs
Many hermit crabs surround a crown conch snail

One hermit was already inside the conch shell. The other hermit was on top of the shell and looking for access. Watch my short video of these hermits with the conch snail, which is not the greatest, but shows what is happening in the picture above.

A hermit crab had crawled down inside the shell – even though the conch was still inside! I don’t know if the conch was alive but the shell was not vacant. It appeared to me that the hermit crab was shoving the snail out of it’s home.

If this is the case, then did the hermit crab kill the conch? It would also explain the abundance of hermit crabs in the area. After all, if they have to sit around and wait for an empty shell, it could be a long wait. Why not just oust the snail and grab the shell?

hermit inside a live conch
Both the conch and hermit crab inside the shell!

I took a bunch of photos and have chosen the best to share here. You can see the legs of the striped hermit crab holding on, and wrapping round, the snail. I don’t know if the snail is still alive, but the crab pushed it’s way in even though the shell was occupied by the shell-maker. Did the snail die (for some reason – and was not eaten) and the crab was disposing of the body? Or did that crab cause the snail’s death?

The crown conch snail has black splotches, which can be seen in these pictures, although the foot seems shriveled (see my photo below of a live crown conch snail). The hermit crab was tucked way down behind the conch. I touched it’s legs and it didn’t care. He held on tightly to the snail, which also was not moving.

The Black Speckled Foot of the Crown Conch

The foot can be seen on another crown conch that I found a while back. In the photo below the foot is emerging from the spiky shell. That conch was alive, and it leads me to believe that the one pictured above may have been dead. The foot is yellowed and shrunken. But, did the snail die on it’s own, or did the hermit crab have something to do with that?

crown conch foot
Photo of a living crown conch snail – see the black speckled foot

The Mighty Grip of the Hermit Crab

By the way, those hermit crabs have a mighty grip. Not long ago we visited this same island and I saw many big tulip shells. One shell had a hermit crab inside who was tightly holding onto a pear whelk. It seemed that the pear was empty, and the hermit had such a tight grip that I could hold these shells off the ground by pulling on the tip of the whelk. He was not going to let that shell go!

I can’t imagine why, since the hermit was already in a very nice shell. Do they covet every empty shell they see? There may have been another hermit crab inside the pear whelk, but I didn’t see one. Almost all hermit crabs I see are the striped variety.

hermit inside tulip holding pear

So my question is, do hermit crabs kill marine snails just to take over their shells? I’m not sure why a snail would simply die. Aren’t they usually eaten by birds or other snails? Of course, I don’t know and maybe snails do die of other causes.

Then again, if hermit crabs are killers, it would explain the huge number of them living inside seashells in this area. More observation and investigation, on my part, is needed. One thing is for sure. Both the hermit crab and snail were in the shell at the same time.

Answering the Question – Maybe

The book Spirals in Time, The Secret Life and Curious Afterlife of Seashells (this is an Amazon affiliate link) has some information about hermit crabs. On page 138, the author Helen Scales writes, “The one thing that hermit crabs never do is kill the occupant of a shell before moving in.” She is a marine biologist based in England.

I believe in scientific studies, but isn’t it possible that a few hermit crabs may have gone rogue and become impatient with waiting for snails to die? They have claws. And some of the hermit crabs I’ve seen are pretty large.

With a large population of hermit crabs in the area, finding empty shells to inhabit must be tough. Maybe the hermit crabs in this area are desperate enough to become resourceful in new ways. They will die without a shell to live in.

In closing, never buy hermit crabs as pets, or pick one up from the beach to take home. Being in captivity shortens their life, by a lot. And their existence is miserable compared to being in the wild. Read more about why it’s a bad idea here.

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