Gorilla Crabs – Are They Reef Tank Safe?

Almost all reef aquariums have live rock, and while live rock is beneficial to keeping your aquarium healthy, they also harbor various hitchhikers. One common hitchhiker is the gorilla crab, a hairy and cheeky crustacean known to cause extreme damage inside aquariums.

Gorilla crabs are not reef tank safe and should be removed from your reef aquarium the second you spot one. Gorilla crabs are pests that hitchhike their way into reef aquariums, growing large, and causing havoc wherever they go.

What Are Gorilla Crabs?

Gorilla crab

Gorilla crabs are a group of crabs from the family Xanthidea, and if you haven’t guessed by the name already, they are particularly hairy members of the group. As Xanthid crabs are one of the most diverse crab families in terms of species richness (currently, there are over 500 known species!), their names are often used interchangeably. 

The gorilla crab gets its name from the hair-like fluff that covers its entire body. The color and how much hair the gorilla crab has depends on the species. For example, some can have brown, tan, or green hair covering their entire body, while other gorilla crabs may only have a small amount of hair on their legs, claws, and shell (carapace). The crabs with less hair are commonly known as stone crabs, but they are also members of the Xanthid crab family.

The gorilla crab often starts out small, but it doesn’t take them long to grow much bigger and prey upon corals and fish, which is why they are not reef tank safe

Another thing we should mention is their poison. Most Xanthid crabs are poisonous, containing lethal concentrations of tetrodotoxin in their muscles and eggs. So, don’t try and eat a gorilla crab! While the toxin can be enough to kill you, it is unlikely. But sadly, the same can’t be said for your fish, it will likely be the end of your fish inside the reef tank if they take a nibble on a dead gorilla crab.

One thing we know for certain is that gorilla crabs are hitchhiking champions, making their way into reef tanks around the world, uninvited. 

Are Gorilla Crabs And Emerald Crabs The Same?

As emerald crabs look very similar, they can easily be confused with gorilla crabs. The main difference is that emerald crabs are entirely green including the claws (hence the name), while gorilla crabs have distinctive black-tipped claws. 

Emerald crabs hitchhike their way into reef tanks on live rock, the same as the gorilla crab, but emerald crabs are reef tank safe and can even be beneficial as they eat algae.

Are Gorilla Crabs Good Or Bad For Reef Aquariums?

Many species of crabs hitchhike their way into reef tanks, and while many crabs are harmless and pretty good at assisting your reef tank cleanup crew to keep your aquarium nice and tidy, gorilla crabs are bad news for ANY reef tank. 

Gorilla crabs are omnivores, therefore, they will eat anything they can get their fuzzy claws on. That means coral, invertebrates, clams, anemones, and even slow-swimming fish will not be safe inside your reef tank if a gorilla crab has snuck inside. So, if you spot one, it is essential to plan your ‘operation removal’ asap!

Gorilla crabs may be small, often growing larger with age, but no matter the size of this particular pest, they are all extremely difficult to remove from a reef tank. Once a gorilla crab has found the perfect hiding spot, they tend to stay there, only making an appearance at night. They are also fairly feisty crabs, known for dashing back into their lair whenever you try to catch them. 

If you don’t act fast, it’s bad news, as their hiding spot will soon become an underwater graveyard. As the gorilla crab makes its hiding spot home, it will constantly scrape away the live rock and corals to make the area cozier. This active scraping will eventually destabilize the live rock structure, causing the aquascape to partially or completely cave in. 

How To Remove Gorilla Crabs From Reef Aquariums?

Gorilla crabs

As gorilla crabs have no known reef aquarium predators, your only option is to remove them yourself.

Removing a gorilla crab is easier said than done, and it is often a frustrating exercise, typically ending up with you having to remove the entire aquascape to get them out.

Gorilla Crab Spear

The most common and successful way to remove a gorilla crab is to either kill them or use a gorilla crab spear. A spearing tool such as tweezers, chopsticks, a scalpel, or anything else you have handy that will crush or remove the gorilla crab will do the trick! 

Wait for the gorilla crab to come out of its lair. This is most successful when the lights are switched off, so the gorilla crab thinks it is night. To your frustration, the gorilla crab is likely to be near the entrance to its den, ready to shoot back in as soon as it sees you approaching. So, once the gorilla crab is out in the open, you will need to act fast if you want to successfully catch it.

If your crab has sought refuge in an area with overgrown coral and lots of live rock, it may be too difficult to spear it without damaging other aquatic life. If this is the case, you may consider a trap.

Gorilla Crab Trap

The next best thing is a gorilla crab trap. Aquarium traps are easy to set up and are often one of the easiest ways to remove them from a reef tank. Fish tank crab box traps allow you to catch gorilla crabs without harming them. Crab traps are most successful when the lights are out. 

Using A Shot Glass Trap

To use a shot glass, place the bait (we recommend anything meaty) inside of the glass and place the glass on the bottom of the reef tank with the right side up. 

If all goes to plan, the gorilla crab should climb up the side of the shot glass, falling inside to catch the bait. Because shot glasses have smooth sides, the gorilla crab will not be able to climb back out.

If your gorilla grab is too large for a shot glass, you can use a glass jar.

Using A Shop-Bought Trap

Shop-bought reef traps are great as they are sanitary, easy to use, and can be reused. There are different types of traps available, but for crabs, we recommend the traps that sit on the bottom of the reef tank. This way, the gorilla crab can easily access the box. 

Bait is placed inside the box. Once the crab enters the box, the trap door shuts behind it, capturing the crab inside the box. 

Once you have captured the gorilla crab, take a good look around your reef tank, as the chances are, that if there is one, then there are more!

However, gorilla crab traps are not always successful. As the crab trap needs to be baited, other tank inhabitants have been known to get trapped inside. The trap may take a couple of days to lure the gorilla crab. In the meantime, if anything else gets stuck inside the trap, ensure you release it asap to reduce stress. 

How To Prevent Gorilla Crabs?

As mentioned, gorilla crabs hitchhike their way into reef tanks. The only way to prevent gorilla crabs is to thoroughly inspect live rocks before adding them to your reef tank. We also recommend soaking newly added corals and live rock to remove pests.

Summary

Reef tanks make the perfect addition to any home or office, yet, keeping an aquarium doesn’t come without some issues. One issue is unwanted pests, commonly known as “hitchhikers”. These are creatures that make their way into reef tanks on live rock. While some hitchhikers cause no harm, gorilla crabs do. 

Gorilla crabs are not reef tank safe, so if you spot one inside your aquarium, you must get rid of them immediately with a trap or spear. To prevent them from entering your reef tank in the first place, remember to inspect any newly added live rock and corals.

  • Darby Bonner

    As a marine biologist, scuba diving instructor, and experienced aquarium hobbyist, I am obsessed with everything from corals to cruising pelagics like sharks, and everything else in between.

    darbybonner@gmail.com Bonner Darby

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