8 Things to Know Before Getting a Halloween Moon Crab

When I first got Halloween moon crabs as pets, there was little information out there about them. Here’s what I’ve learned over the past several years.

Shiva, in all her glory. Photos by: Kirsti Stephenson
Shiva, one of my Halloween moon crabs, in all her glory. Photos by: Kirsti Stephenson

My introduction to the wondrous world of Halloween moon crabs was a complete surprise to me.

One evening a few years ago, 2 of my colleagues in the broadcasting and film industry showed up on my doorstep with a unique belated birthday gift: a 10-gallon tank with 3 of the most incredible-looking crabs I had ever seen. The colleagues had found them at a reptile store and told me they were called Halloween moon crabs.

Loving all living creatures, especially unknown ones, I was elated but hesitant. I didn’t have a clue how to feed or care for these curious, clacking critters.

Like so many pet store owners looking to make a sale, the guy at the reptile store had assured my friends that the crabs needed no special food, heat or substrate requirements other than newspaper, water and table scraps.

I was fascinated by these crazy-colorful crabs, who were approximately 10 times the size of my strawberry hermit crabs and had black bodies with brilliant orange legs, jack-o’-lantern white-rimmed, protruding eyes and dangerous-looking purple claws that they happily raised into a sparring position if any uninvited fingers intruded.

I hand-fed them some leftover roast beef, which they delicately placed into their tiny jaws via their pincers. I went to bed that night with wild dreams of decorating their cage the next day and naming them in my head.

I Was On My Own

The first order of business was to do some online research about my new family members to learn about their origins and care requirements.

But I found little information on how to care for these crabs in captivity other than the fact that they were land crabs with the scientific name Gecarcinus quadratus and were found mainly along the Pacific Coast in places like Mexico, Costa Rica and southward to Panama.

No luck at the bookstore, either. The only book in the World’s Largest Bookstore in Toronto was a thin How to Care for Land Hermit Crabs, with half a page at the back of the book dedicated to the Halloween moon crab that described them only in their natural habitat.

I found a few online posts from people in the United States who had tried and failed to raise them successfully in captivity. I was on my own with 3 new charges that I was determined to give the best life possible.

Shiva did a full exoskeleton molt — it looks like she cloned herself! Halloween moon crabs usually molt deep underground, and to see a complete, perfectly intact molt is rare.
Shiva did a full exoskeleton molt — it looks like she cloned herself! These crabs usually molt deep underground, and to see a complete, perfectly intact exoskeleton is rare.

8 Things to Know About Halloween Moon Crabs

The following advice is what I’ve learned over the past 8 years through trial and error and a concerted effort to duplicate the crabs’ wild habitat as closely as possible.

1. Moon crabs like to fight each other.

They are difficult to sex, but within the first 2 years I unfortunately lost one of my crabs to an overnight brawl with a bigger crab, who I believe was a male.

2. A 10-gallon tank with newspaper substrate is unacceptable.

These crabs require enough space to burrow deep into the moist (but not damp) substrate to molt, which they do several times a year and shed their entire exoskeleton in 1 piece.

My 2 crabs Dante and Shiva happily reside in a 50-gallon fish tank with a handmade screen top for ventilation and to protect them from escape and injury.

They should be called “Houdini crabs” — they are agile climbers and can be found in the wild up tropical trees and in bushes.

3. Foster their natural climbing instinct by providing wood branches or faux foliage.

This will allow them to climb freely in their habitat. I recommend cork bark, which is readily available at most pet stores. It is light and retains water when you spray the enclosure to help create a humidified environment conducive to the crabs’ ability to molt.

Cork bark comes in a variety of shapes and sizes and can act as shelter for your crabs as well as a climbing medium. It’s moderately priced, long-lasting and will not rot like found wood gathered outside your home will.

Take a closer look at a beautiful Halloween moon crab:

You can also use half coconut shells for aboveground housing. The crabs will not try to eat plastic plants and will enjoy the scenery and climbing opportunities.

4. They can go as deep as 3 feet to create a network of underground burrows.

They do this for shelter and brumation close to a water source, usually on the banks of a river, ocean or estuary.

5. They are nocturnal.

Moon crabs hunt and forage at night, and they are buried or hiding during the day.

6. Moon crabs live on land but always near water.

They require access to both fresh and saltwater pools that are big enough to climb in and out of but not deep enough for them to drown — these crabs do not swim.

I use filtered or spring water to avoid the chemicals added to tap water. I refill it every other day in a 7-by-4-inch BPA-free Tupperware container with rocks and shells on the bottom to help the crabs get in and out safely.

Moon crabs must have access to fresh water at all times to moisten their gills.

7. They also need to have a smaller container filled with a teaspoon of raw sea salt diluted in hot water.

This provides them with the salt content for their diet that they require and would get in the wild.

8. Like most crustaceans, moon crabs require a regular source of calcium to fortify their exoskeleton (shell).

I have found that either placing a dish of Reptivite or similar powdered calcium brands mixed into their food is sufficient. But I like to keep a cuttlefish bone in their enclosure. They love to meticulously scrape off chunks with their pincers and ingest it.

* * *

There’s more! In Part 2 of this article, I will go more in depth about caring for Halloween moon crabs. I’ll share what I’ve learned about substrate, temperature/lighting and what to feed them.

Kirsti Stephenson

View posts by Kirsti Stephenson
An animal lover and herpetologist, Kirsti Stephenson volunteers with many conservation groups. She has many pets, from a Cornish Rex cat to sugar gliders, Halloween moon crabs, snakes, geckos, a bearded dragon and a door mouse, and she is a foster mom to chicks and ducklings to be released as adults to a local educational farm in her hometown of Toronto.

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