Crabs, a remarkably ancient species dating back more than 400 million years, hold a prominent place in the animal kingdom. Surpassing even the era of dinosaurs, crabs have persisted for approximately 200 million years. Our planet is home to nearly 850 distinct crab species, exhibiting an astonishing array of around 4,500 unique variations.
Should you desire to delve deeper into the secrets of the crab’s extraordinary longevity, you have arrived at the ideal destination.
Taxonomically speaking, crabs belong to the decapod order of crustaceans, characterized by possessing five pairs of legs on their upper body. Every crab falls under this decapod classification. Notably, one or more of these appendages undergo a remarkable transformation, evolving into a formidable pair of pincers or claws. Additionally, crabs possess a protective exoskeleton known as a carapace, which encompasses both their head and thorax, resulting from their fusion.
Taxonomy of Crabs
The intricate task of categorizing all living organisms on our planet falls under the domain of taxonomy, a branch of scientific study. Through the process of taxonomy, living creatures are grouped together based on shared characteristics, with increasing specificity as we descend through the hierarchy. This hierarchical system encompasses various levels of categorization.
Now let us explore the taxonomy of crabs:
Kingdom: Animalia – All multicellular animals, including crabs, are encompassed within this kingdom.
Phylum: Arthropoda – Insects, spiders, and crustaceans, all possessing segmented bodies, external skeletons, and jointed limbs, belong to this phylum.
Subphylum: Crustacea – Aquatic arthropods that possess four or more pairs of limbs modified into pincers fall under this subphylum.
Class: Malacostraca – Crustaceans, including crabs, exhibit compound eyes, often stalked, as a distinguishing feature.
Order: Decapoda – The head and thorax of decapod crustaceans, such as crabs, are protected by a carapace, which are fused together.
Suborder: Pleocyemata – Female pleocyemata crabs retain fertilized eggs on their specialized swimming legs, known as pleopods, until they hatch, exhibiting a unique method of incubation.
Infraorder: Brachyura – Crabs classified under this infraorder possess bodies with shortened abdomens that fold beneath them, contributing to their distinctive appearance.
Apart from their taxonomic classification, crabs can also be further categorized into four main groups, denoting additional aspects of their classification.
Dromiacea
The distinguishing characteristic used to classify crabs within this particular group is their last pair of legs. These thoracic legs undergo a transformative process, resulting in a pair of articulated pincers that are positioned closer to the crab’s posterior. These modified pincers serve various functions, including gathering shells to fortify their carapace and showcasing their intricate dexterity during feeding.
Within this collection, there exist 240 present-day crab species alongside 300 extinct crab species. The oldest known fossil belonging to this group was discovered in the Jurassic period approximately 200 million years ago, offering us a glimpse into the ancient origins of these remarkable creatures.
This specific group of crabs is classified as
Raninoida
The distinctive feature of the crab superfamily we’re discussing lies in the unique appearance of their abdomen compared to other crab species. Within this superfamily, there are 182 known species, representing four genera and four families.
These remarkable crabs have been present on Earth for approximately 145 to 166 million years, tracing their origins back to the Cretaceous period. They have stood the test of time, witnessing the ebb and flow of geological eras.
In order to navigate their surroundings, these crabs employ a swimming technique known as drag-powered swimming. This method involves the crab propelling itself through water by paddling in a circular, horizontal motion. Just as one rows a boat, these crabs exert force on the water, pushing it backward to generate propulsion.
Cyclodorippoida
Within this group of crabs, there exists a lone superfamily known as Cyclodorippoidea. This superfamily comprises three distinct families: Cyclodorippidae, Cymonomidae, and Phyl lotymolinidae. Each of these families shares a common ancestry and exhibits unique characteristics and traits within the realm of crab classification.
Eubrachyura
Among the diverse world of crabs, there are two notable categories that stand out for their heightened physical and intellectual development. These categories are known as Heterotremata and Thoracotremata, and they are distinguished based on the positioning of their genital openings.
In Heterotremata, the males possess genital openings located on their legs, while the females have genital openings situated on their sternum. This disparity allows for easy differentiation between the sexes within this group.
On the other hand, the crabs belonging to Thoracotremata exhibit a different arrangement. Both male and female crabs in this category have genital openings present on their sternum, providing a common feature for both genders.
These remarkable groups of crabs have an extensive history that traces back to the Bathonian period, which occurred roughly 168 to 166 million years ago. They have withstood the test of time, evolving and adapting throughout the ages.
Mating
During the process of mating, crabs become more susceptible to predators, especially when they engage in mating immediately after molting. Molting refers to the shedding of their rigid outer shell, which reveals a newly formed, softer shell underneath.
Choosing to mate after molting is a strategic decision for crabs due to the challenges posed by their hardened exoskeletons during the mating process. By waiting until after molting, crabs can mate more effectively and with greater success.
In the mating ritual, male crabs assume a protective role. They cradle and accompany female crabs that are approaching the molting stage. Even after mating, the male remains by the female’s side, ensuring her safety until she regenerates her exoskeleton, offering her additional protection.
Following mating, the female crab carries her eggs beneath her abdomen. These eggs are typically observed as a cluster of orange, sponge-like substances situated beneath the crab’s carapace. The female diligently safeguards and nurtures these eggs until they are ready to hatch.
While the specific details may vary among different crab species, the basic life cycle of crabs follows a similar pattern. Crabs go through distinct stages of development and growth, ultimately reaching adulthood.
A typical crab’s life cycle consists of the following stages:
- Eggs
- Zoea (larval stage)
- Megalopa (transitional larval stage)
- Juvenile Crab
- Adult Crab
To delve further into the specifics, let’s explore the life cycle of a blue crab as an example.
The Zoeal Stage
When blue crabs hatch from their eggs, they bear little resemblance to their mature form. They enter the world as microscopic larvae known as zoea.
In habitats with high salinity, young blue crabs can be found drifting in the water column. They sustain themselves by consuming microalgae and smaller larvae present in their surroundings.
During the larval development of a blue crab, it progresses through seven distinct stages. The transition from larva to adult crab takes place over a span of 31 to 49 days as it passes through these developmental stages. While there are similarities between the larva at each stage, they gradually grow in size.
Like their adult counterparts, crab zoea possess exoskeletons and must undergo molting to accommodate their growing bodies. Through this molting process, they shed their old exoskeleton and replace it with a larger, more adapted one, enabling them to continue their development.
The Megalopal Stage
Once the larval stage is completed, the juvenile crab enters the megalopal stage, during which it starts to take on a more crab-like appearance. This phase can last anywhere from 6 to 20 days.
During the megalopal stage, the juvenile crab’s body undergoes significant growth. Legs begin to emerge from the sides of their body, gradually becoming wider. While their elongated abdomen from the zoea stage is still present, it now stretches out behind their developing crab form.
Unlike the zoea larvae, which freely float in the water column, megalopas prefer environments with lower salinity and ample hiding spots. They seek out estuaries, where they can more easily find food resources. They navigate these areas by utilizing the ebb and flow of tides, taking advantage of the movement in and out of the estuary.
The Adult Form
Once the crab reaches the estuary, it will undergo molting to assume its adult form, measuring approximately 2 mm (0.2 cm) in length.
As an adult, the blue crab will reside within the estuary. During the summer months, they tend to molt more frequently, but their molting frequency decreases in colder temperatures. Eventually, the crab will reach sexual maturity and undergo a significant molt known as the “terminal” molt, marking the final molt in their life cycle. Following this final molt, the crab ceases to grow further.
The terminal molt coincides with the mating process. After mating, the male crab will remain in the estuary for the remainder of its life. In contrast, the female crab will venture to areas with higher salinity to prepare and nurture the eggs. This divergence in habitat allows the female to provide optimal conditions for the development of her offspring.
Eggs
Female blue crabs have the ability to store sperm for an extended period, up to a year, and are highly selective about where they choose to lay their eggs. This allows them ample time to find the optimal location before releasing their eggs. They have the capability to mate during the winter months and delay the extrusion of their eggs until the summer season if needed.
During the process of egg extrusion, fertilization occurs as the eggs pass through the crab’s body and reach the “apron,” which is a curled-under section of the abdomen specifically adapted for depositing eggs. This apron area may exhibit small appendages where the eggs attach themselves.
An egg mass can contain millions of eggs, with clutch sizes reaching up to 8 million. Initially, the egg mass appears orange due to the abundance of yolks in the eggs. As the eggs develop and the larvae consume the yolks, the color of the egg mass darkens. After approximately 1 to 2 weeks, the eggs hatch, initiating the next stage of the crab’s life cycle.
However, it’s important to note that only a minute fraction of the eggs, approximately 0.0001%, will ultimately reach maturity. The journey to adulthood poses numerous challenges, resulting in a high attrition rate for the developing larvae.
Diet
A striking African or Nigerian rainbow crab, scientifically known as Cardisoma armatum, is captured in a photograph. It displays vibrant colors of blue and red while partially facing the camera, showcasing its prominent right claw. The crab’s eyes sit atop eyestalks, providing it with a heightened sense of vision.
Crabs exhibit diverse dietary preferences, which can vary depending on their habitat and species.
The majority of crabs are considered omnivorous, meaning they consume a combination of plant and animal matter. As opportunistic scavengers, they possess an insatiable appetite and will eagerly consume any available food source. The diets of crabs encompass a wide range of items, including:
- Detritus: Crabs feed on decomposing plant debris or the remains of deceased fish.
- Snails: These shelled creatures form a part of the crab’s diet.
- Algae: Some crabs consume various types of algae.
- Live plants: Certain species of crabs may include live plants in their diet.
- Barnacles: Crabs are known to feed on barnacles.
- Shrimp: These crustaceans are a favored prey item for many crab species.
- Worms: Some crabs incorporate worms into their diet.
- Other crabs: In certain instances, crabs may prey upon other crabs.
These examples provide an overview of the wide-ranging food sources that crabs may consume to sustain their nutritional needs.
Natural Predators
Crabs possess a formidable defense mechanism in the form of a hard shell, providing protection against predators. However, despite this armor, they remain vulnerable to various predators in their aquatic habitats.
Larger and more aggressive fish such as bass, halibut, cod, and sharks are among the notable predators that readily prey upon crabs. These fish possess the strength and predatory skills to consume crabs as part of their diet.
Invertebrates, including octopi, are also avid crab consumers. With their hard and sharp beaks, octopi have the ability to tear open crab shells, making them formidable predators. A single bite from an octopus can be lethal to a crab, often paralyzing it before it can mount any defense.
Sea turtles pose a significant threat to crabs as well. With their enormous and powerful jaws, sea turtles can effortlessly crush crab shells, making them dangerous predators.
Crabs must also contend with the predation risk posed by other creatures within their environment. Sea otters and seals, known for their voracious appetites, can consume significant quantities of crabs in a single day. Additionally, crabs are susceptible to being preyed upon by various ocean-dwelling creatures.
Furthermore, crabs face threats from within their own species. Larger crabs often target their smaller cousins, preying upon them. In certain cases, even crabs of similar size and species can display cannibalistic behavior, posing a risk to one another.
During their larval stage, crabs, especially small fish, rays, and eels, face heightened vulnerability to predation. These early stages of development make them particularly susceptible to being preyed upon by various predators in their environment.
Habitat, Migration, & Range
Crabs exhibit a diverse range of shapes and sizes, showcasing remarkable variations across the globe. Different crab species display preferences for specific water temperatures, with some thriving in cold waters while others favor warmer environments. They can be found in various aquatic habitats, including freshwater, saltwater, and brackish water. Interestingly, certain crab species have even adapted to terrestrial environments and can be encountered on land. This incredible adaptability allows crabs to inhabit a wide array of habitats, showcasing their remarkable versatility.
Blue Crab Habitation
Most research on crab migration has focused on blue crabs, which exhibit an extensive range along the US Atlantic coast, stretching from Nova Scotia to Argentina, including northern New England.
Male blue crabs tend to favor estuaries and tributaries with lower salinity levels, while females are more commonly found in or near water, showing a preference for higher salinity levels compared to males.
In these oceanic regions, blue crabs seek shelter in underwater grasses and oyster reefs. They are particularly drawn to warmer and shallower waters. However, when temperatures become too cold for their comfort, they burrow into the muddy silt, using it as protective cover.
While climatic changes can induce crab hibernation, they undertake migrations for various reasons, primarily associated with mating and reproduction. When a female blue crab is prepared to lay her eggs, she embarks on a migration toward saltier waters, as mentioned earlier in previous sections.
Red Crab Migration
An intriguing example of crab migration can be observed in the crimson crab, which inhabits the lush forests of Christmas Island. When the time for reproduction arrives, these crabs undertake a remarkable journey from the forests towards the ocean. During this period, one can witness a breathtaking sight as thousands of crimson crabs traverse roadways, streams, and beaches in their determined quest. It is a spectacle that showcases the incredible movement and collective behavior of these fascinating creatures
Impact of Climate Change
The impact of climate change extends to crabs, as it affects various species across the globe. Rising ocean temperatures, in particular, have significantly influenced crab populations in the Pacific Ocean, according to George Somero, the director and professor at Stanford University’s Hopkins Marine Station.
A Crab Survey conducted in the 1930s involved meticulous identification of every marine invertebrate within a 95-square-yard (79-square-meter) area of the Pacific Grove marine lab. When the survey was repeated in 1993, it revealed a striking change over just six decades. The northern crab species had experienced a drastic decline, while the number of southern crab species had increased, with eight out of nine southern species being identified.
Continued warming of ocean waters due to climate change is expected to drive northern-living crabs to migrate further north in search of cooler waters. Species adapted to cooler environments have a limited “thermal tolerance” and may suffer detrimental effects when exposed to warmer waters. Thermal stress can lead to issues with the heart and nervous system, potentially proving fatal for these crabs.
If ocean temperatures continue to rise at the current rate, the Earth could experience an additional increase of 6 degrees Fahrenheit in the next 50 years, posing an even greater threat to northern crab populations.
To determine heat tolerance levels, Somero and his team conducted experiments comparing crabs in intertidal and subtidal habitats. Their findings indicated that intertidal-living crabs, which are exposed to fluctuating conditions, are significantly more vulnerable to the impacts of global warming than their subtidal counterparts. Intertidal-living crabs along the Pacific coast are already at high risk of surpassing their thermal limits, making them particularly susceptible to the consequences of rising ocean waters.
Cultural Symbolism of Crabs
Crabs hold significant symbolic and emotional power in various cultures, particularly among indigenous communities. They are often associated with themes of life renewal and regeneration.
Within tribal beliefs, a captivating notion is that crabs possess an ability to perpetually renew themselves. Instead of dying, they are believed to bury themselves in the sand or earth, undergoing a process of regrowing their shells. This cyclical transformation connects them to the moon, which in turn lends them the astrological sign of “cancer.”
The enduring symbolism of crabs in these cultural contexts encompasses themes of resilience, rebirth, and the eternal cycles of nature. Their perceived ability to regenerate and their connection to celestial bodies inspire profound interpretations and associations within indigenous belief systems.
Commercial Fishing
Fishing boats of varying sizes, ranging from 25 to 280 feet (8 to 85 meters) in length, can be spotted engaging in crab trapping activities. The process involves deploying pots or traps, which are connected to floating buoys and lowered into the water.
In shallow waters, trapping techniques can be employed at depths of up to a thousand feet (305 meters). Wire squares arranged in a grid pattern are commonly utilized as traps. These traps are baited to entice the crabs inside. After a day or two, the fishermen return to retrieve the traps. Using hydraulic blocks, they lift the traps out of the water, completing the process of crab harvesting.
Types of Crabs
When it comes to determining the most delicious crab species, opinions may vary, but there are five commonly agreed upon by many eateries. These crabs are not only highly regarded for their taste but are also widely found and abundant worldwide. It’s no surprise that these species are the most commonly enjoyed and consumed by people around the globe.
1. Blue Crab
The scientific name for blue crabs is Calinectes sapidus, and they are commonly referred to as “lovely swimmers.” These crabs possess specialized “fins” that resemble paddles, enabling them to navigate through the water column. These fins are actually flattened back legs that aid in swimming.
In addition to their delectable taste, blue crabs are visually stunning in their natural habitat. Their legs boast a striking dark blue coloration, while their shell exhibits a light turquoise hue. These colors may vary as the crabs undergo different stages of their life cycle. When prepared for consumption, their shells turn a vibrant crimson, hence their name derived from the hue of their bodies.
As one of the most widely consumed crab species, blue crabs are abundantly found along the eastern coast of the United States. They inhabit the seas of the Atlantic Coast, ranging from the Gulf of Mexico to the shoreline. Furthermore, blue crabs can also be found in select locations in Argentina. Their prevalence and popularity as a culinary choice make them a familiar sight in these regions.
2. Dungeness Crab
The Dungeness Crab boasts a broader distribution range compared to the blue crab. From the waters of Alaska to Baja, Mexico, these crabs can be found along the Pacific coast. The town of Dungeness in Washington State was the first to harvest and introduce them as a culinary delicacy.
While they inhabit and are caught along the entire coast, the majority of the Dungeness Crab catch, about 70%, comes from the waters of California, Oregon, and Washington.
These crabs are required to meet certain criteria for harvest, including a minimum size of 6.25 inches (1.60 meters), with males being the preferred catch. However, they can grow up to lengths of 10 inches (0.3 meters). The color range of their shells varies from dark brown to purple.
Despite their popularity among restaurant patrons, getting Dungeness Crabs to the table is not a straightforward task. These crabs possess remarkable skills in evading capture, adept at slipping past guards unnoticed and mastering the art of disguise to avoid traps and pits.
3. Snow Crab
The snow crab goes by various names, with the most accurate being Cancer quanbumi.
One of its popular names, the rock crab, reflects its preference for dwelling in the depths of the ocean. Along the east coast of the United States, it can be found in coastal waters.
Due to its long, slender legs resembling those of a spider, it is also referred to as the spider crab. It is sometimes called the “queen crab” due to its impressive leg span, although it is not as long as that of the king crab.
Snow crabs are highly prized and sought after in culinary preparations, commanding a significant price. They are primarily harvested in Alaska, Japan, Canada, and Maine, with these regions being the main sources for this valuable crab species.
4. King Crab
King crabs earned their name due to their astonishingly large size. Scientifically known as Paralithodes camtschaticus, these majestic creatures can grow up to 10 feet (3.05 meters) in length and weigh as much as 25 pounds (11 kilograms).
To put their dimensions into perspective, their legs alone can stretch up to five feet in length. Despite their imposing leg span, their black-red carapaces reach a modest length of around 11 inches (0.3 meters), with the majority of their body size accounted for by their remarkable legs.
The abdomens of king crabs possess such distinctive features that they are often referred to as the “tail” of the animal, adding to their intriguing characteristics. Positioned at the rear of the shell, the “tail” is fan-shaped in appearance.
With legs of such considerable length, each pair serves a specific purpose. While king crabs have five sets of legs, they primarily use the central set for walking. The front two claws house the powerful pincers, with the right pincher being the most robust. The two small legs positioned at the back, tucked beneath the carapace, assist in sperm transfer and the cleaning of embryos, highlighting their specialized functions.
5. Florida Stone Crab
The “Florida” stone crab, despite its name, can be found along the western North Atlantic Ocean from Connecticut to Belize. While they are most commonly encountered off the coast of Louisiana, the Bahamas, and in salt marshes of Georgia and South Carolina.
Sea crabs possess a remarkable ability to regenerate missing limbs, giving them an advantage over predators. When faced with an attack from a predator like a grouper, they can simply detach their limb and leave it behind. Remarkably, these crabs can regrow their lost limbs, coming back even stronger than before.
Stone crabs are highly sought after in restaurants due to their delectable flavor, often described as a delightful blend of lobster and shrimp.
It’s important to note that while crabs are a common ingredient in many diets worldwide, not all crabs are edible. There are indeed poisonous crab species that should be avoided for consumption.
6. Xanthid Crabs (Mosaic Crab, Toxic Reef Crab, & Shawl Crab)
The Xanthidae crab family, notably recognized by a subset with black-tipped pincers, is home to the majority of venomous crab species. However, it’s important to note that these crabs do not naturally produce the toxins, and not every member of this family is toxic. Given that some crabs within the same species lack toxicity, researchers speculate that the toxins originate from the crabs’ diet or perhaps symbiotic bacteria.
It’s impossible to contract the poison from a Xanthid crab through touch as these creatures lack spines and aren’t capable of biting. Therefore, ingesting them is the only way one could potentially be poisoned.
Two of the deadliest toxins known to exist in nature, saxitoxin and tetrodotoxin, may be stored in the muscle tissues and egg clusters of Xanthid crabs. To illustrate the potency of these toxins, it’s worth noting that a mere half a milligram is lethal enough to kill an adult human.
Despite the strength of these toxins, they are resistant to heat and remain in the crab’s tissues even after cooking, meaning cooking these crabs doesn’t neutralize the toxins.
Luckily, these crabs are exclusively found in Australia and don’t generally form part of most people’s diets. Furthermore, these crabs are typically small in size, reducing the risk of them being mistaken for more commonly consumed crab species.
7. Emerald Crabs
Emerald Crabs, named for their attractive hue, are a type of saltwater crab often found in domestic aquariums due to their preference for bubble algae. Their vibrant coloration not only appeals to human aesthetics but also serves as a warning of their inherent toxicity, making them one of the most visually striking crab species.
Although they possess toxicity, they don’t pose a significant threat to humans. Like their relatives in the Xanthidae family, their poison only becomes harmful if consumed. Considering their small size—maxing out at around 5 centimeters (or 2 inches) in diameter—Emerald crabs are not considered a viable food source.
In their natural habitat, these crabs inhabit the warm Caribbean waters of the Gulf of Mexico. They have a penchant for seclusion, often hiding amongst caves, rocks, and crevices within coral formations.
8. Floral Egg Crab
Distinct from others, this type of venomous crab boasts black-tipped pincers. They feature a slim, oval shell that ranges from shades of brown to black and can be spotted in the waters of the Indo-Pacific Ocean. Their carapace is adorned with intricate white or yellow lines that resemble lace. Interestingly, they have a habit of embellishing their shell with various objects they come across.
These crabs possess large, oval-shaped claws and a shell that is notably wider than its length. Even at their smallest, they measure about 10 centimeters (or 4 inches) in length.
Equipped with extremely slender legs and no specialized swimming appendages, it’s evident that these crabs aren’t designed for long-distance travel. Instead, they use their legs to maneuver within their immediate environment.
Floral egg crabs have a wide distribution, found across Southeast Asia and the Indo-Pacific region, extending down to Australia.
Crabs are a diverse group, encompassing a broad range of forms and dimensions, with some species naturally outscaling others. However, in the world of crabs, the Japanese spider crab stands unrivaled in terms of sheer body size.
9. Japanese Spider Crab
You might have imagined the king crab to be quite colossal, but when compared to the Japanese spider crab, the king crab pales in size.
This creature is not only the largest crab species on earth, but it also holds the title of the largest crustacean out of the 60,000 crustacean species globally.
Japanese spider crabs can reach an impressive body length of up to 16 inches (0.4 meters). Their ten long legs, each measuring around 18 inches (0.5 meters), contribute to their large overall size. These gentle behemoths can tip the scales at a hefty 42 pounds (19 kilograms).
Their oval, spiky shells exhibit striking shades of orange and white, making them conspicuous. However, their coloration allows them to blend seamlessly into their rocky, seafloor habitats.
Spider crabs are native to the Pacific coast of Japan, inhabiting depths ranging from 164 to 1,640 feet (50-500 meters). They thrive in temperatures around 50 degrees Fahrenheit (10 degrees Celsius).
While we’ve just discussed the largest crab in the world, the Japanese spider crab, it stands to reason that there must be a smallest crab somewhere on the other end of the scale.
10. Pea Crab
Pea crabs, with their tiny bodies measuring a mere 0.75 inches (0.02 meters) in length, hold the title for the smallest crab species globally.
“Pea crab” is a term used to describe any crab from the Pinnotheres genus, which includes species that inhabit polychaetes, mollusks, and echinoderms. Rather than feeding off its host like a parasite, the pea crab seeks shelter and protection from the creature it inhabits.
Pinnotheres maculatus is a variety of pea crab that resides in the mantle cavities of clams, mussels, and scallops. Pinnotheres pisum, another pea crab, can be found living in mussels and cockles in the shells of coastal European waters.
While some crabs are aquatic, others are land-dwellers or semi-terrestrial, showcasing the diversity within the crab species.
11. Blue Land Crab
Known as the “giant” land crab or the blue land crab, this species is the largest semi-terrestrial crab found in Florida. Despite their “giant” moniker, their carapace only measures about 6 inches (0.15 meters) in diameter.
In their early stages, these crabs sport a dark brown, purple, or orange hue, which lightens as they mature. Eventually, their color transitions to a blue-grey shade as they age. Similar to many other crab species, one of their pincers is noticeably larger than the other.
While blue land crabs spend the majority of their life on land, they are dependent on water for survival and reproduction. When they are not near water, they reside in burrows they’ve dug themselves, which can be several feet deep.
Contrary to the carnivorous habits of many crabs, these land crabs are primarily herbivores. They have a preference for a plant-based diet, feasting on leaves, berries, flowers, fruit, and vegetables over animal matter.
12. Coconut Crabs
While the Japanese spider crab holds the title for the world’s largest crab, the coconut crab reigns as the world’s largest land-living arthropod and the largest terrestrial crab species.
Coconut crabs boast impressive three-foot-long legs and are capable of carrying weights up to 62 pounds (28 kilograms)—a testament to the power of their pincers.
Unlike many other crabs, coconut crabs, which are a type of hermit crab, don’t need to rely on shells for protection due to their substantial size. Once they’ve grown sufficiently, they abandon the need for an external shell, relying instead on their sturdy exoskeleton for defense.
These giant crabs are native to the Indo-Pacific region and can be found in locales ranging from the Gambier Islands in the Caribbean to the coasts of Africa and the Eastern Pacific Ocean.
True to their name, coconut crabs have a penchant for coconuts, which they actively seek by climbing trees. But their diet isn’t limited to coconuts; they also consume fruit, nuts, seeds, and even animal matter. Unlike most crabs, which predominantly feed on carrion, coconut crabs are known to hunt live prey such as rats, birds, and even other crabs.
13. Hermit Crabs
There are over 800 distinct species of hermit crabs distributed worldwide. While most hermit crabs are aquatic, there are several terrestrial species frequently adopted as pets.
Despite their name, hermit crabs are not true crabs. They actually bear a closer resemblance to lobsters. A true crab is characterized by a uniformly hard exoskeleton and the ability to generate its own shell.
Unlike true crabs, hermit crabs possess a hard exoskeleton only on the front half of their bodies. They rely on a scavenged shell to safeguard their soft tail-end. Generally, they seek out empty shells, but in the absence of such, they’ve been known to kill snails and other gastropods to obtain their shells.
Given that hermit crabs don’t naturally produce shells, they have a specialized, hooked tail that enables them to lodge securely within the borrowed shell. To accommodate their growing bodies, they need to periodically molt and shed their shell.
Crabs Kept in Aquariums
14. Fiddler Crabs
Fiddler crabs are among the most popular crab species kept as pets in aquariums. With their compact size of 2-3 inches (0.05-0.07 meters) and fascinating growth process, they offer an engaging spectacle for onlookers. Males are recognized for their one significantly larger pincer on their front legs, which they wave in a dance-like motion to either attract mates or ward off threats.
Fiddler crabs come in a range of colors, from subtle to vibrant, and some species even lack the ability to see.
If you’re considering adopting a fiddler crab as a pet, there are a few key things you should be aware of. Fiddler crabs require brackish water—a mix of fresh and saltwater—for survival, as they cannot live in either completely fresh or fully salty water. Being semi-terrestrial creatures, they also require access to land. Providing an environment with ample rocks or decorative elements allows them to easily come ashore when desired.
Given their need for air access and brackish water, many enthusiasts opt for a species-specific tank for their fiddler crabs. However, if your aquarium is large enough, brackish water-compatible fish, such as mollies, can be housed in the submerged part of the tank.
15. Thai Micro Crab
Thai micro crabs, renowned for their exquisite appearance, are among the smallest creatures in the world, with their bodies measuring a mere 0.4 inches (0.01 meters) wide. Their virtually transparent bodies, tinted with a subtle grey-brown hue, make them challenging to spot as they tend to blend seamlessly into their surroundings.
These tiny creatures are best suited to smaller aquariums, ideally less than five gallons. Although they can coexist with certain mild-mannered fish species, they thrive best in the company of other micro crabs or shrimp, which do not pose a threat to them. Their diminutive size makes them susceptible to predation by larger aquatic inhabitants.
Unlike fiddler crabs, Thai micro crabs are strictly freshwater creatures, and should not be housed in brackish or saltwater aquariums.
16. Anemone Crabs
Anemone crabs are one of the most frequently found crab species in saltwater aquariums, winning many admirers with their striking coloration. Their shells feature a unique pattern of red polka dots around the edges, set against a white porcelain backdrop.
These crabs have fan-like limbs which they use for feeding, and large claws for grasping and consuming pieces of flesh they encounter. They employ their fan-like appendages to capture tiny food particles from the surrounding water, sweeping them through the water column in a manner reminiscent of a feather duster.
With their vibrant colors and distinct feeding behavior, anemone crabs are a delight to observe. They are named after anemones, their preferred habitat. Although anemone crabs can survive in a home aquarium without an anemone, they will undoubtedly be more content if one is present.
Other Common Crab Species
17. Horseshoe Crab
Contrary to what their name implies, horseshoe crabs aren’t true crabs at all. These creatures are invertebrates that closely resemble crustaceans and belong to the arthropod group.
Despite their significant size, horseshoe crabs are often kept as pets in home aquariums. They can reach lengths of up to 24 inches (0.61 meters) and widths of 12 inches (0.3 meters), with a weight around 3 pounds (1 kilogram).
They prefer residing in shallow waters and are distributed across the Atlantic and Eastern Pacific oceans. Horseshoe crabs inhabit shallow estuaries and continental shelves, avoiding deeper waters. Their range extends from Maine to the southern Yucatan Peninsula in Mexico.
Horseshoe crab blood plays a crucial role in the medical field as it’s used to test for bacterial contamination in pharmaceuticals. They are often caught to have their blood drawn before being released back into the water. Regrettably, this harvesting process has adversely affected horseshoe crab populations, with a mortality rate of 15-30% among the released crabs.
18. Brown Crab
As indicated by their name, brown crabs exhibit a brown hue with a slightly reddish undertone. When cooked for consumption, their shells transition to a lighter brown shade. Their claws, tipped in black, present a stark contrast to their overall coloration.
The shells of these crabs are uniquely shaped, appearing oval with wavy edges, sometimes referred to as a “pie-crust”.
Brown crabs have a relatively large carapace, ranging between 6-9 inches (0.15-0.22 meters) in length, which is quite large compared to many crab species. These crabs can weigh as much as 6.6 pounds (3 kg).
These crabs inhabit a variety of aquatic environments, including the North Sea, the Northern Atlantic Ocean, and the Mediterranean Sea.
19. Horsehair Crab
These crabs are characterized by their brown and orange coloration, with their bodies speckled with orange spots. Their shells have a rugged texture, and their bodies are covered with prickly hairs.
With a length ranging from 3.9-4.7 inches (0.09-0.12 meters) and a weight not exceeding 2.2 pounds (0.99 kilograms), these crabs are relatively small in size.
Their habitat extends from Alaska to northern Japan, with a preference for colder waters. They are benthic creatures, dwelling at depths reaching up to 350 meters (1,148 feet), making them inhabitants of the ocean floor.
20. Peekytoe Crab
The Peekytoe crab, alternatively known as the Atlantic rock crab, is a species adapted to cold-water environments. It gets its unique name, “Peekytoe”, from the pointed shape of its legs and the brown color of its shell, which is sprinkled with purple spots.
This crab is of moderate size, with a diameter approximately around 5.25 inches (2.4 meters) long.
Interestingly, Peekytoe crabs were once considered a nuisance by lobster fishermen, as they often got caught in their nets unintentionally. However, around the year 1997, they began to be valued by chefs and sought after, marking a shift from being discarded as an unwanted bycatch.