Crabs have a bit of a bad reputation in the aquarium hobby. We’ll admit it, they can be destructive! But not all crabs are bulldozers (and some of the ones that are can still be worth it).
Looking for a crab to add to your (reef) tank? You’ve come to the right place. From the good to the bad to the anemone slingers, these are the species you might find at your local aquarium store — and what kind of system they’re right for.
| Common Name | Right for you if you want a… |
|---|---|
| Green Emerald Crab | Small, algae-eating janitor crab |
| Arrow Crab | Impressive, colorful crab |
| Pom Pom Crab | Reef-safe nano crab |
| Porcelain Anemone Crab | Docile, reef-safe crab |
| Blue-Legged Hermit Crab | Micro crab clean-up crew |
| Halloween Hermit Crab | Showstopper, peaceful hermit |
| Spider Decorator Crab | Wacky oddball crab |
Green emerald crab (Mithrax sculptus)
Many aquarists refuse to keep any crabs beside the green emerald crab in their tanks. We’ve got to say that despite their appearance (let’s be honest, they’re kind of ugly), we really love ’em too.
None of the bad stuff we associate with crabs applies to this one — no fish hunting or bulldozing action here. It might pick at sessile invertebrates, but will get along with cheap and fast-growing corals just fine.
The best thing is that green emerald crabs don’t just make excellent neighbors, but also double as cleaning crew members. Like all inverts they’ll happily clean up after your fish, and for such a small critter, they also have an impressively big taste for algae. They’re among the only aquarium inhabitants that will eat annoying bubble algae!
| Minimum tank size | 10 gallons |
| Reef-safe? | Mostly |
| Difficulty level | Easy |
Arrow crab (Stenorhynchus seticornis)
Is that a sea spider?! Nope, just an arrow crab! Despite their arachnid appearance, these critters are actually true crabs; you can recognize them by their stripey suit, tiny blue claws, and the “horn” sticking out of their faces.
Although they’re only tentatively reef safe and are known to catch smaller invertebrates like reef shrimp and snails if left to go hungry, we think these impressive crabs are worth making a few accommodations for. It’s pretty cool to see them move around on those spindly legs, plus they make excellent bristleworm hunters.
Keep in mind that despite their small bodies, arrow crabs can reach a leg span as wide as an adult human hand. The females stay a little smaller than the males, but we still wouldn’t recommend them for nano tanks or desktop reefs — they really do need some space.
| Minimum tank size | 30 gallons |
| Reef-safe? | Not really |
| Difficulty level | Intermediate |
Pom pom crab (Lybia sp.)
All crabs are kind of weird, but this one might be the wackiest of them all. The pom pom crab is also known as the boxer crab, two common names it lends from the fact that it carries a small anemone on each claw. Thanks to its tiny size, this is one of the best crabs for a desktop nano reef (and also the funniest to look at).
The pom pom crab’s anemones serve multiple functions: it can raise them in defense when threatened and it also uses them to mop up food. If it loses one or both of its symbionts, it’ll try to frag itself a new pair or even attempt to steal them from another pom pom crab!
Although this crab’s anemones do sting and could accidentally hit corals, they’re really too small to do any damage. Other aquarium inhabitants won’t be bothered by a pom pom crab unless they get a bit too inquisitive, nor are your hands in any danger.
| Minimum tank size | 5 gallons |
| Reef-safe? | Yes |
| Difficulty level | Easy |
Porcelain anemone crab (Neopetrolisthes maculatus)
Here’s another crab that maintains a symbiotic relationship with anemones, although this one lives in them instead of carrying them around the reef. Although the porcelain anemone crab’s claws are huge, they’re not very useful for fighting, so it instead relies on the anemone’s stinging tentacles for safety.
If you’re looking for a truly docile invert that will leave both corals and its tankmates alone, porcelain anemone crabs are the way to go. Although they’ll try to chase away anyone who gets too close to their host, we’ve never seen them do any real damage; they mostly try not to interact with their neighbors at all.
Worried an anemone will be too much of a hassle? You could try the bubble tip anemone, which is much less finicky than the carpeting species, but rest assured that something like a torch coral also works fine.
The crabs mostly find their own food on their hosts tentacles, though you can drop some food nearby one or twice a week. You’ll also see them using their filter claws to help themselves to some of the coral or anemone’s powdered meals whenever you feed it.
| Minimum tank size | 10 gallons |
| Reef-safe? | Yes |
| Difficulty level | Easy |
Blue-Legged Hermit Crab (Clibanarius tricolor)
Here’s another excellent option for a desktop reef! Although hermit crabs aren’t technically true crabs, we think they’re close enough. Given their popularity, especially the smaller species like the blue-legged hermit, it seems most aquarists are inclined to agree.
The great thing about these tiny hermits is that they come with none of the caveats of true crabs. They’re peaceful and, whether fish, shrimp, or coral, don’t bother their tankmates. The only creatures they occasionally harass are snails, but you can prevent those from being evicted by scattering plenty of empty shells around the tank.
Thanks to their appetite for detritus and algae, small hermit crabs like blue legs make great additions to your underwater cleaning crew. In larger systems, they can make do with what they find scavenging and won’t need supplemental feeding.
In smaller tanks, throw in the occasional invertebrate pellet; if you keep multiple crabs, they’ll all bumble over and cause a pile-up of shells trying to get to the food first.
| Minimum tank size | 5 gallons |
| Reef-safe? | Yes |
| Difficulty level | Easy |
Halloween Hermit Crab (Ciliopagurus strigatus)
How seasonally appropriate is this stripey hermit crab? If blue-legged hermits are too small for your liking, the striking Halloween hermit might be a better choice for you. Thanks to its larger size (up to 2″ excluding shell) and beautiful colors, this one’s sure to draw all eyes to your reef.
Like blue-legged hermit crabs, Halloween hermits come with all of the good and very little of the bad of crabs. They focus on gunk and algae instead of corals, and leave most tankmates — except snails — alone. Do offer yours regular meals to make sure it stays well-behaved.
Although Halloween hermit crabs can live in a variety of homes, they specialize in cone snail shells. Most other hermits don’t fit in these shells because their opening is very narrow, but Halloween hermits are flat enough to wiggle their way in.
We don’t recommend trying to harvest your own cone shells — the snails’ venom can be fatal to humans. Store-bought definitely wins this time.
| Minimum tank size | 15 gallons |
| Reef-safe? | Yes, just clumsy |
| Difficulty level | Easy |
Spider Decorator Crab (Camposcia retusa)
Talking about Halloween-appropriate invertebrates… the spider decorator crab might not sport the perfect spooky season colors, but it sure takes its costume very seriously. Unless you notice its eyes or see it move, it’s easy to mistake this crab for a random piece of reef rubble.
As their name suggests, spider decorator crabs aren’t born like this: they decorate themselves. Those perfect camouflage costumes do in fact consist of pieces of reef junk stuck to their thick hairs. These tidbits can include broken shells, macroalgae, sponge, and even coral polyps.
Now, we won’t lie and say spider decorator crabs make good reef pets. They don’t just pick up loose pieces of debris, but will also use their claws to snip off whatever they think helps them blend in. To make matters worse, they’ll also snap up and eat any small or slow-moving tankmates they can get their claws on.
Despite all this, we think these crabs more than worth setting up a novelty tank and sacrificing a few cheap coral frags for. Seeing it wear them as a hat is just priceless!
| Minimum tank size | 20 gallons |
| Reef-safe? | No |
| Difficulty level | Easy |
Tip: There’s the good and the ugly… and then there’s the irredeemable. Worst of all is the gorilla crab, a common hitchhiker known for snatching fish and demolishing corals. If you find one of these in your tank, you might want to get rid of it; find out how to recognize and remove them in our gorilla crab guide.
Conclusion
A marine aquarium filled with colorful fish and funky crabs like the ones we’ve discussed here is an amazing sight to see. There are so many species to choose from! If you’re not sure where to start, though, aquarium set-up and maintenance can be daunting tasks.
FantaSEA can help: we’ll design, build and maintain your tank for you, so all you have to do it enjoy it. Just contact us with your ideas and we’ll bring them to life.
