Fun Emerald Crab Facts For Kids | Kidadl


Fun Emerald Crab Facts For Kids

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The emerald crab is also known as Mithrax crab or green clinging crab. This crab's scientific name is Mithraculus sculptus. The emerald crab is a nocturnal, and saltwater invertebrate that usually does the cleaning crew job. It's a scavenger that feeds on wasted / uneaten meaty foods as a food source. Its diet consists of all types of nuisance algae, bubble algae (Velonia so.), coralline algae, and meaty foods like snails, shrimp, corals, small fish, or marine fish available on reefs environments. These crabs are semi-aggressive in dense or higher concentrations tanks or aquariums. Hence advisable to keep one crab in a 20 to 25-gallon marine aquarium/tank. These crabs species are tolerant to their tank mates and highly compatible in reef environments. But intolerant to changes in water parameters and copper-based medication.

These crabs are naturally found in caves, services, or under the rocks or cling to corals reef. These Mithrax crabs are native of the Caribbean tropical Sea in the Gulf of Mexico region and do not have any possible threats; hence they are not evaluated or not listed under Conservation Status.

If you are fascinated by aquatic life, want to learn more. Then you might want to check out our website for exciting facts on Dungeness crabs and blue crabs.

Fun Emerald Crab Facts For Kids

What do they prey on?

Algae, snails, small fish, polyps, marine waste

What do they eat?


Average litter size?

100-1000s eggs

How much do they weigh?

28.2 oz (0.80kg)

How long are they?

1.6-2.5 in (4-6.3 cm)

How tall are they?


What do they look like?

Dark green, streaks in red, blue-white, black, and gray

Skin Type

Exoskeleton shell

What were their main threats?

Large Marine Fish, Reef-associated Hawkfish

What is their conservation status?

Not Evaluated

Where you'll find them?

Marine Reefs


Atlantic And The Caribbean Sea In The Gulf Of Mexico









Emerald Crab Interesting Facts

What type of animal is an emerald crab?

The green emerald crab is a marine or saltwater invertebrate that is highly compatible with coral reef environments. They can also be kept in a marine home aquarium under optimal water conditions. And being nocturnal, these species are active during the night, and during the morning, they hang out in their hiding places such as caves or under the rocks.

What class of animal does an emerald crab belong to?

Emerald crabs belong to the class of Malacostraca (the common class for lobsters, shrimp, and crabs) in order Decapoda under the family of crabs (Majidae).

How many emerald crabs are there in the world?

Emerald crabs are abundant in nature and also sold in the pet trade. Each female crab produces hundreds or thousands of larvae as their production rate is higher; however, the exact population size is not documented.

Where does an emerald crab live?

The emerald crab is a native crab of the Caribbean Sea in the Gulf of Mexico, and this species can see its existence from the Bahamas, Southern Florida to the Northern part of Brazil at a depth of 177 ft (53.9 m) on corals reef. Moreover, these green crabs are commonly found in the marine tank or home aquarium as they eat bubble algae, types of nuisance algae, and clean the algae forming in tanks.

What is an emerald crab's habitat?

Emerald crabs are marine or saltwater invertebrates commonly found on coral reefs, caves, cervices, or rocks where they hide during the day. These green crabs are nocturnal where breeding activities and feeding during the night. These crabs are notorious eaters; hence, the most suitable habitat would be shallow water with changing variations in water conditions that help the growth of algae and rocks for coral's polyp to attach themselves.

Who do emerald crabs live with?

Emerald crabs are semi-aggressive and notorious feeders; however, their stay with corals reef-associated sea animals, sea anemones, polyps, coral's starfishes. These green crabs are peaceful as long there is no competition for food.

How long does an emerald crab live?

Emerald crabs live for two to four years in the wild; however, they can live a couple of years more in a captive environment like an aquarium or marine tanks if proper care is taken like diet, water parameters, breeding, and avoiding crowding so they can live peacefully.

How do they reproduce?

Reproduction is one of the exciting aspects of the emerald crab. The male crab mounts on the female crab and gets into the lock position throughout the mating process. After mating, this female green crab does not lay eggs, but it has a pouch under its belly where eggs are stored, and the female crab releases the tiny baby crabs directly into the water. Then, the young emerald crab molting takes place where it sheds a skull like an exoskeleton and hides under rocks till a sturdy exoskeleton is formed.

What is their conservation status?

The emerald crab conservation status is Not Evaluated. The production rate is very high, where each female crab produces around a thousand baby crabs in one breeding season.

Emerald Crab Fun Facts

What do emerald crabs look like?

Emerald crabs have hairy legs

The Mithrax crab is bright green (emerald) color. It grows up to 2.5 in (6.3 cm) in size. The carapace is long, flat, shiny, where legs and claws are assembled. Like any other crabs, these species have four pairs of hairy legs, and the two claws are long and spoon-shaped, and the claw tips bear white spots. The protruding eyes are located on the carapace just above the mouth. The male and female crab exhibits sexual dimorphism, but it's pretty difficult to notice by ordinary people except for specialists like crustaceologists. The baby crabs that are released from the mother's pouch are usually white cream in color.

How cute are they?

The shiny green crabs look attractive and petite. Their cute appearance and the beneficial skill to clean bubble algae in tanks and aquarium helps the pet owners. As a result, these species have demand in pet trade where it sells for $7-$9.

How do they communicate?

These green crabs are semi-aggressive and eat viciously. The actual means of communication of these species is unknown. However, few studies on crabs, in general, have some peculiar techniques to communicate, like claws and leg-rubbing that produces stridulation sounds. In addition, ghost crabs use their gastric stomach mill to produce stridulation sounds to communicate their agitation.

How big is an emerald crab?

The emerald crab grows up to 2.5 in (6.3 cm) in length, and they are two times bigger than reef gobies named Trimmatoms with just 0.39 in (0.99 cm) in length.

How fast can emerald crabs move?

Emerald crabs usually sit on reef rocks or cling to coral polyps during the day. And at night, they usually walk around in search of food. The exact speed of the emerald crab is not documented; however, it can cover more than 800 ft (243.8 m) in one hour.

How much does an emerald crab weigh?

Green bubble algae eater crabs are small, and they weigh 28.2 oz (0.80 kg) approximately.

What are the male and female names of the species?

Emerald crabs do not have sex-specific names. They are commonly referred to as female and male crabs.

What would you call a baby emerald crab?

Emerald crab babies do not have specific names. They are commonly called larval crabs or zoea larvae.

What do they eat?

Emerald crab is a notorious eater. They eat all meaty foods and waste fish debris lying on the reef. Hence they make good scavengers that clean their surroundings. They are also referred to as cleaning crew. Their diet consists of Mysis shrimp, snails, smaller fish, zooplankton, seaweed nori, leafy foods, krill, coral polyps, sea anemones, spirulina. In addition, they eat bubble algae, live microalgae, hair algae, and all types of nuisance algae. These crabs also enjoy in-tank or aquarium fish pellets food. Other small fish may be a victim.

Are they harmful?

Emerald crabs are not harmful to humans. However, they can hurt with their claws. Much smaller fish can be the victims of the clattering claws of these bubble algae eaters. On the other hand, if there is sufficient food for these aquarium cleaners, they may be peaceful sitting on corals reef.

Would they make a good pet?

These green crabs make excellent pets as they are natural tank or marine aquarium cleaners. However, they have specific water parameters to maintain. As a result, these species are common in the pet trade.

Did you know...

Optimal temperature requires 75-80 F0 (23.8-26.6 C0 ) and pH range 8.4.

The ideal condition required for algae growth is nitrates below 10 PPM, calcium 420-440 PPM, alkaline 8-9.5 DKH, magnesium of 1260-1350, and phosphate level below 10. If phosphate levels are high, it can affect the water and fish species in the tank. Then it's time to change the water.

Although these green Mithraculus sculptus are hardy but still need acclimation before dropping them in the tank.

There are many aquarium cleaners, shrimp, and fish available. For example, skunk cleaner shrimps, coral banded shrimp, and neon goby.

Are emerald crabs hardy?

The Mithrax crab is a hardy and valuable crustacean. Although they survive in the saltwater aquarium, they have a brutal survival instinct and can quickly adapt to temperature changes. In the wild, although they are small in size, they can withstand strong currents in the ocean.

The emerald crab's compatibility

In the case of the emerald crab species, it's always advised to keep one crab in the aquarium and very few crabs in large tanks as they become aggressive if there is competition for food and can kill small fish. These species can be compatible with big predator fish as they hide in corals. And over algae growth in the tank also may not be suitable for them to accommodate.

Here at Kidadl, we have carefully created lots of interesting family-friendly animal facts for everyone to discover! Learn more about some other crabs from our land crab facts and hermit crab facts pages.  

You can even occupy yourself at home by coloring in one of our free printable Emerald crab coloring pages.

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