A week after adding the live rock and the snails to my new marine aquarium, I found the remains of one of my beautiful banded trochus snails scattered on the rocks in my tank. The shell was broken into pieces.
The remains of a snail. Did it die of natural causes, or was it a victim of murder?
I immediately blamed the creepy crab with his big claws. I asked the experts here at the office, and they agreed to disagree. I got all kinds of responses. “Most crabs are scavengers.” “Never trust a hitchhiker.” “It depends what shape and color the tips of his claws are.” “When in doubt, take it out.”
I saw him climb into one of his rock caves and I decided that was my chance to remove him. I took the rock out of the tank and put it in a small bucket filled with water from the tank. (I didn’t want to kill the guy, if he was innocent.) I drove to the local store with my rock and crab, to see if the experts there could vouch for the crab’s character.
In a way they did. They couldn’t get him out of his little rock cave to get a good look at him, but they said it’s unlikely that a crab would break the shell of a snail. He may eat a snail if he’s really hungry, but even then, he wouldn’t break up the shell. So we pronounced Mr. Crab innocent of the charges and I took the rock home and put it back in my tank.
Later that evening, Mr. Crab emerged from his cave and ate the food I had put in the tank. He also scooped the fine coral sand into his mouth with those big scary claws. On closer inspection, I saw that the tips of his claws are shaped like spoons. Presumably, they’re for scooping sand, not killing things. I’m so glad I gave him the benefit of the doubt!
Crab with the snails
So who killed the snail? Is there still a murderer at large in my tank? The people at the store said to be on the lookout for a mantis shrimp that may have come along with the live rock. The Mantis shrimp kills its prey by breaking the shells of invertebrates. They are really scary looking and notoriously difficult to catch.
A few weeks later, I was watching the crab, and to my horror, I saw him ambush a small hermit crab, flip it over, and murder it! It was traumatic to watch! My tank is very deep, so there was no way to just reach in there and stop him. He jabbed those scary claws into the shell, and then he slinked away and left the empty shell behind. Now I see that the spoon shape at the end of his claws come in handy for scooping crabs and snails out of their shells.
So now I knew he was guilty of one murder for sure, and could easily commit more. He had to go. So I waited for him to go back into his rock cave, and when he did, I pulled the rock out of the tank and put it in a bucket of tank water. It didn’t take long for him to climb out to investigate the food I put in the bucket. I removed the rock, and took the crab back to the store.
One associate said he’s a calico rock crab. The truth is there are so many species of crabs in the ocean that any species could show up on live rock. Either way, all of them agreed that he is bad news. “The bigger he gets, the bigger his prey will be,” they said. That was the last I saw of Mr. Crab. I left him at the store. It made me sad to say goodbye to him.
A month has passed, and I’m happy to report that I have NOT found any more empty shells.
Crab picking something up with is claw