Reef Hermit Crab 101:

Hermits are one of the most interesting denizens of the reef aquarium. Sometimes they get a bad rap, but for the most part I think this is misdeserved. Below is a write up of my experiences with the various hermit crabs I have kept in my reef. I've tried to give as much info as I can based on my experiences... Your mileage my vary!

2011 update: I've got a "non-reefsafe" hermit in my reef right now! He has been in there a few months and has caused no trouble so far. He is about an inch in size and insanely colored. Above is my artist rendering. I haven't got a good, in-focus shot of him yet. He is pretty secretive and only comes out when I feed the fish with some pe mysis.

Clibanarius tricolor, "Blue Leg Hermit"

One of the most common hermits in our tanks. Often purchased TINY, this crab stays small, only growing to about 1 inch in size. Hailing from the Caribbean, they are rumored to voraciously eat snails. I believe they only eat snails when they are starving! They starve when you have too many crabs and not enough algae. Commonly wears small Cerithium and Astraea shells.

Paguristes cadenati, "Scarlet Reef Hermit"

Ahh. The scarlet hermit: sissy of the hermit crab world. This crab stays small, only growing to about 1.5 inches. It is also pretty to look at and is relatively peaceful. Is it any wonder this is such a popular hermit? The scarlet usually costs more than the more common dwarf species (zebras, blue legs, et al.). In the past, I have paid 2 - 5 dollars each. I have read in various places that they eat cyano, but have never witnessed this during any of my cyano outbreaks.

Calcinus elegans, "Electric Blue Hermit"

From the Indo-Pacific. Also called the "Blue Knuckle Hermit". Grows pretty large... 2 inches or more. They are a little more aggressive than your average "dwarf" hermit, but I have never had a problem mixing smaller crabs with them. They are more expensive than most other hermits. I paid $5 each for mine, some places sell them for as much as $10 a piece. You will need some larger shells available for these guys. Turbo shells and Red Footed Conch shells work well.

Medium sized Electric Blue and Adult Mexican Red Tip, for comparison.

Calcinus elegans, Hawaiian Variant

Sometimes wrongly identified as the Halloween Hermit, see below. The Hawaiian morph seems to grow slowly in my experience.

Calcinus tibicen, "Orange Claw Hermit"

These are my favorite hermits!! From the Caribbean, they often come in with shipments of blue legs, so they are cheap. I paid a buck each for mine. You have to have a sharp eye to see them in the dealer's tank. I found mine at an LFS. These get rather large and aggressive like the electric blues, but again, no problems with them and smaller hermits other than a little intimidation. These things eat hair algae like it is going out of style!

Calcinus laevimanus, "Hawaiian Zebra Hermit"

These exotic looking hermits come from Hawaii, obviously. They get a little bigger than blue legs or Mexican red tips, but they are still a relatively small species. Zebra hermits are also called left handed crabs because one claw is bigger than the other. This is a trait common to all crabs of the Calcinus genus. Usually cheap, they are pretty small when you buy them. Make sure to have some small shells for them to play in. These are able to run really fast backwards when a larger hermit comes near. They are comical to watch, their blue eyes stand out against their black and white coloration.

Clibanarius sp., "Mexican Red Tip Hermit"

Another common, cheap hermit. The fish stores around me don't stock it on purpose, but they get mixed in sometimes. You can get them for a buck or less most places online. Stays very small, less than 1 inch. The one I had rode out Hurricane Katrina in my sump. After the storm, it got into my overflow and was in there for a few weeks before I got it out along with my spotted mandarin and orange spot blenny who had also jumped in! Pretty hardy little critters.

Clibanarius sp., "Unidentified Hermit"

This is another common Caribbean hermit, coming in mixed with blue legs. The ones I have owned seem to stay pretty small, growing a little larger than the blue legs. They typically reside in Cerithium and Astraea shells. I can't seem to find a species name for it at all, only the genus. I think it is so boring that they haven't gotten around to officially describing it yet. This is a VERY hardy species.

"Unidentified Hermit"

I have no clue as to the ID on these guys. I came across these in a batch of blue leg hermits, so I assume they are from the Caribbean. I have seen them offered for sale (CHEAP), labeled as "right handed hermits" at a website dedicated to critters from the Florida Keys. I'd hazard a guess that they stay small, similar to blue legs. The ones I have had were all in Cerithium shells. One claw is way LONGER than the other. Their legs are also longer than average. They are mostly colorless, with thin tan bands on their legs. I like to call these: "Albino Blood-Sucking Spiders from Mars". Kind of creepy looking, they are a VERY active hermit and can move pretty darn fast. They are aggressive and do a great job of eating detritus and micro algae from the live rock.

Update: mine all died after a few months in my tank.

"Unidentified Hermit"

Here is the other crab in my tank that I have NO CLUE as to its ID. I have seen them in a few stores, mixed in with Scarlet Hermit shipments. The one I had was small, in a Cerith snail shell. It is yellowish in coloration and has a velvet-like appearance. Sort of fuzzy looking. Both claws are tiny like a scarlet hermit. I have talked to another person who had a larger one and they said that the crab grew fast in their tank and was semi-aggressive.

Ciliopagurus strigatus, "Halloween Hermit Crab"

*   Not my crab or photo.

These come from the Indo-Pacific. I have seen them offered for sale labeled as collected in Hawaii. Some say they are reef safe, some say not. I have heard they eat cyanobacteria. They are also said to reach an adult size of "several inches". This genus appears to have 7 species that appear similar. Some seem to have a thick body (like the crabs from Calcinus) and some appear to have a thin body (like the crabs from Dardanus). The thin ones (like this picture) often wear Conus shells. I haven't seen a shot of a thick one in a shell, only preserved.

Dardanus guttatus, "Blue Knee Hermit"

*  Not my crabs or photo.

From the Indo-Pacific (Vanuatu is one collection site), these omnivorous crabs get large. I have seen them in 4 inch Conus shells. Not considered reef safe. Not sure if it if from their eating habits or just that they get big and can bull-doze things. This particular one seems to be eating meat (like most hermits will).  Also eats cyanobacteria (I have witnessed this in person).

Dardanus megistos, "White Spotted Hermit"

*  Not my crabs or photo.

This crab is not considered "reef safe". As you can see, they get big. They get bigger than this. They are also known as the "Shell Breaker".

Clibanarius vittatus, "Thin Stripe Hermit"

*  Not my crabs or photos.

Eventually grows large (fist sized), so shouldn't be considered reef safe. Doesn't seem to bother corals but has been reported to eat feather dusters and snails. Make sure you have LARGE shells on hand. May do best in aggressive fish-only type tanks. These can survive in cooler temperature waters. They are often collected on beaches and piers in the south-eastern USA. | Photos by Dave Harms unless otherwise noted.