The king crab is not a true crab like the Dungeness or snow crab. Instead, it is more closely related to the hermit crab.
The blue king crab, like all king crabs, is a decapod, or “ten-legged,” crustacean with a unique “tail,” or abdomen, that is shaped like a fan and tucked under the back of the shell. In addition, they have five sets of legs. The first set has their claws or pincers; the right claw is usually the biggest on adults. The next three sets are their walking legs, and the fifth set is small and usually tucked under the back of their carapace (shell). Adult females use these special legs to clean their embryos (fertilized eggs), and males use them to mate with females by transferring sperm.
The blue king crab is about the same size and shape as the more common red king crab, except for its color. However, blue king crabs usually only lay eggs every two years, and their eggs are a bit bigger. Large female blue king crabs might not be able to get the energy they need for ovary development, growth, and egg release every year because of things in their environment that make it hard for them to do so, like poor quality or scarce food or less feeding activity because the water is cold. Blue king crabs can get very big, and the Pribilof and St. Matthew island areas are generally very productive. This, however, is not in line with environmental restrictions. While the fertilized embryos are in the egg cases attached to the pleopods under the female crab’s abdomen, they grow. Hatching happens from February to April. Once the larvae are out in the wild, the big female blue king crabs will molt, mate, and push out their clutches in late March or early April of the next year.
Female crabs need about 29 days to lay their eggs, and they lay about 110,000 eggs each time. The larvae live in the water and go through four zoeal stages that each last about 10 days. The length of time depends on the temperature; the development slows down when it’s cold and speeds up when it’s warm. Stage I zoeae need to find food within 60 hours because going hungry makes it harder for them to catch prey and molt. Zoeae consume phytoplankton, the diatom Thalassiosira spp. in particular, and zooplankton. The fifth stage of development is the non-feeding and transitional glaucothoe stage. During this stage, the larvae change into the shape of a small crab but can still swim by using their long abdomen as a tail. At this stage, the larvae look for a good place to settle down. Once they find it, they molt into the first juvenile stage and stay benthic from then on. The larval stage is estimated to last for 2. 5 to 4 months and larvae metamorphose and settle during July through early September.
Blue king crab molt frequently as juveniles, growing a few millimeters in size with each molt. Unlike red king crab juveniles, blue king crab juveniles are not known to form pods. A female king crab is sexually mature when she is about five years old, while a male may not be sexually mature until he is six years old.
Because crabs don’t have hard parts that stay in place through molts, no one knows how long they live. Estimates of 20 to 30 years in age have been suggested.
Food eaten by king crabs varies by species, size, and depth inhabited. A lot of different sea creatures, like worms, clams, mussels, snails, brittle stars, sea stars, sea urchins, sand dollars, barnacles, crabs, other crustaceans, fish parts, sponges, and algae, are known to be eaten by king crabs.
Many animals eat king crabs, such as fish (Pacific cod, sculpins, halibut, yellowfin sole), octopuses, king crabs (which can eat each other), sea otters, and several new species of nemertean worms that have been found to eat king crab embryos.
Adult blue king crabs exhibit nearshore to offshore (or shallow to deep) and back, annual migrations. They come to shallow water in late winter and by spring the females embryos hatch. Some adult males and females molt and mate before they start their migration to deeper waters to find food. Adult crabs tend to segregate by sex off the mating-molting grounds. It is rare for red, blue, and golden king crabs to live together, even though the depths and habitats where they live may overlap.
The blue king crab is an anomuran in the family Lithodidae. The red king crab is Paralithodes camtschaticus, and the golden or brown king crab is Lithodes aequispinus. Blue king crabs live off the coast of Japan’s Hokkaido. Separate populations can be found in the Sea of Okhotsk and along the coast of Siberia to the Bering Straits. This species has been seen in North America in places like Point Hope, the Diomede Islands, the outer parts of Norton Sound, and King Island. In the remainder of the Bering Sea, they are found in the waters off St. Matthew Island and the Pribilof Islands. Blue king crabs live in large, geographically separate groups that are often found near fjord-like bays in more southern areas, all the way to southeastern Alaska in the Gulf of Alaska. The blue king crab is only found in a few isolated areas, while the red king crab is found in many more places. This is likely because of changes in water temperature that happened after the last ice age, which limited the range of this cold-water-adapted species. Some of the things that might be directly limiting its range are its physiological needs for reproduction, competition with the red king crab, which is better adapted to warm water, being pushed out by warm-water predators, or the need for a place for larvae to settle down.
With its massive claws and distinct reddish shell king crab is one of the most prized and expensive seafood delicacies. King crab legs and meat are savored for their sweet succulent taste and meaty texture. But despite the name, king crab surprisingly isn’t a true crab at all.
King crab belongs to a group of crustaceans known as “false crabs” that have evolved crab-like traits over time. While not technically crabs, these imposter crustaceans have adopted similar physical features and behaviors as true crabs.
Below we’ll explore why the king crab earns the crab name despite not being a real crab, how it compares to true crabs, and key facts about this fascinating shellfish.
The Crab-Like Attributes of King Crab
So if king crab isn’t really a crab, why is it called one? Here are some of the major crab-like attributes of king crab that give it a crab appearance and lifestyle:
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Flattened, rounded body – King crab has a wide flat shell rather than a cylindrical body. This gives it a distinct crab silhouette.
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Small folded tail – The king crab’s tail is tiny and tucked neatly under its body. True crab tails are similarly reduced and hidden.
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Sideways scuttling – King crabs walk sideways or diagonally like true crabs, using legs on each side of their body alternately.
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Leg joints bending sideways – A king crab’s leg joints bend sideways instead of forwards and back. This allows for sideways mobility.
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Claw-tipped legs – Their legs end in small claws or pincers, ideal for grasping food and defending themselves.
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Camouflage coloring – Reddish hues help king crabs blend into their environment, much like many real crab species.
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Bottom-dwelling – King crabs live largely on the seafloor, where they scavenge and hunt – typical crab behavior.
So while not closely related, king crabs have adapted very crab-like features over time that allow them to live crab-style lives!
How King Crabs Compare to True Crabs
King crab belongs to an order of crustaceans called Lithodidae, or stone crabs. Here’s how true crabs of the order Decapoda differ:
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Number of legs – True crabs have 10 legs. King crabs have 8 legs and 2 claws (which are really modified legs).
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Tail size – True crab tails are significantly reduced. King crab tails are still prominent but folded under their body.
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Gills – True crabs have gills located in a branchial chamber. King crabs have them exposed on leg joints.
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Reproduction – Unlike true crabs, king crabs still have to mate belly-to-belly. They can’t mate belly-to-back.
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Larval stage – King crab larvae look more shrimp-like than true crab larvae.
So while king crabs are an evolutionary work-in-progress, they’ve achieved enough crab-like adaptations to nearly mimic their distant cousins.
Fascinating Facts About King Crab
Beyond its misleading name, the king crab has many other fascinating features:
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There are 4 main species of king crab living in cold, northern Pacific and Atlantic waters. Red and blue king crabs are the most popular for eating.
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They can reach up to 6 feet claw tip to claw tip and weigh up to 25 pounds. Legs can span over 3 feet long.
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Males have a spiky, spear-likeappendage used to flip rival males during combat.
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Their large leg span and claws make king crabs formidable predators of the seafloor. They eat worms, clams, fish and other crustaceans.
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Fishermen harvest king crabs using large steel cages called crab pots that lure them in with bait.
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Only male king crab legs and claws are commonly eaten. Females are usually thrown back.
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When cooking king crab, the claws can be cracked with lobster crackers or garden shears. Legs can be cut at joints using kitchen shears.
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King crab meat has a sweet, succulent taste. Many love dipping it in melted butter or garlic aioli sauce.
While not a true crab, the king crab earns its royal moniker through its immense size, fierce hunting, and decadent meaty claws and legs.
Why So Many “False Crabs” Evolved
King crabs are just one of many examples of crustaceans evolving crab-like traits independently. This phenomenon is called carcinization. Crabs have arisen from lobster-like ancestors at least 5 separate times over the course of evolution.
Scientists have a few theories as to why carcinization occurs so often:
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The crab shape provides better defensive armor against predators.
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A crab-like body works well for bottom scavenging and hunting.
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The body shape leaves legs free for specialization beyond walking, like paddling or digging.
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Losing the large tail opens up new evolutionary possibilities.
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A flattened body and tilted joints facilitate faster sideways movement.
So while the king crab stops short of being 100% fully crab, its numerous crab-adjacent adaptations give it major advantages in its cold water rock- and mud-bottom habitats.
An Impressive Imposter
With its hulking size, crustacean essence, and succulent sweet meat, the king crab earns the crown for king of crustaceans. Even though it’s technically a “false crab,” the king crab epitomizes what it means to live the crab lifestyle.
Next time you crack open the dramatic legs and claws of Alaskan king crab, appreciate just how delicious carcinization can be! Though not a true crab, the king crab is close enough to bear the name proudly.
Alaska Department of Fish and Game
Jump to species:
The king crab is not a true crab like the Dungeness or snow crab. Instead, it is more closely related to the hermit crab.
The blue king crab, like all king crabs, is a decapod, or “ten-legged,” crustacean with a unique “tail,” or abdomen, that is shaped like a fan and tucked under the back of the shell. In addition, they have five sets of legs. The first set has their claws or pincers; the right claw is usually the biggest on adults. The next three sets are their walking legs, and the fifth set is small and usually tucked under the back of their carapace (shell). Adult females use these special legs to clean their embryos (fertilized eggs), and males use them to mate with females by transferring sperm.
The blue king crab is about the same size and shape as the more common red king crab, except for its color. However, blue king crabs usually only lay eggs every two years, and their eggs are a bit bigger. Large female blue king crabs might not be able to get the energy they need for ovary development, growth, and egg release every year because of things in their environment that make it hard for them to do so, like poor quality or scarce food or less feeding activity because the water is cold. Blue king crabs can get very big, and the Pribilof and St. Matthew island areas are generally very productive. This, however, is not in line with environmental restrictions. While the fertilized embryos are in the egg cases attached to the pleopods under the female crab’s abdomen, they grow. Hatching happens from February to April. Once the larvae are out in the wild, the big female blue king crabs will molt, mate, and push out their clutches in late March or early April of the next year.
Female crabs need about 29 days to lay their eggs, and they lay about 110,000 eggs each time. The larvae live in the water and go through four zoeal stages that each last about 10 days. The length of time depends on the temperature; the development slows down when it’s cold and speeds up when it’s warm. Stage I zoeae need to find food within 60 hours because going hungry makes it harder for them to catch prey and molt. Zoeae consume phytoplankton, the diatom Thalassiosira spp. in particular, and zooplankton. The fifth stage of development is the non-feeding and transitional glaucothoe stage. During this stage, the larvae change into the shape of a small crab but can still swim by using their long abdomen as a tail. At this stage, the larvae look for a good place to settle down. Once they find it, they molt into the first juvenile stage and stay benthic from then on. The larval stage is estimated to last for 2. 5 to 4 months and larvae metamorphose and settle during July through early September.
Blue king crab molt frequently as juveniles, growing a few millimeters in size with each molt. Unlike red king crab juveniles, blue king crab juveniles are not known to form pods. A female king crab is sexually mature when she is about five years old, while a male may not be sexually mature until he is six years old.
Because crabs don’t have hard parts that stay in place through molts, no one knows how long they live. Estimates of 20 to 30 years in age have been suggested.
Food eaten by king crabs varies by species, size, and depth inhabited. A lot of different sea creatures, like worms, clams, mussels, snails, brittle stars, sea stars, sea urchins, sand dollars, barnacles, crabs, other crustaceans, fish parts, sponges, and algae, are known to be eaten by king crabs.
Many animals eat king crabs, such as fish (Pacific cod, sculpins, halibut, yellowfin sole), octopuses, king crabs (which can eat each other), sea otters, and several new species of nemertean worms that have been found to eat king crab embryos.
Adult blue king crabs exhibit nearshore to offshore (or shallow to deep) and back, annual migrations. They come to shallow water in late winter and by spring the females embryos hatch. Some adult males and females molt and mate before they start their migration to deeper waters to find food. Adult crabs tend to segregate by sex off the mating-molting grounds. It is rare for red, blue, and golden king crabs to live together, even though the depths and habitats where they live may overlap.
The blue king crab is an anomuran in the family Lithodidae. The red king crab is Paralithodes camtschaticus, and the golden or brown king crab is Lithodes aequispinus. Blue king crabs live off the coast of Japan’s Hokkaido. Separate populations can be found in the Sea of Okhotsk and along the coast of Siberia to the Bering Straits. This species has been seen in North America in places like Point Hope, the Diomede Islands, the outer parts of Norton Sound, and King Island. In the remainder of the Bering Sea, they are found in the waters off St. Matthew Island and the Pribilof Islands. Blue king crabs live in large, geographically separate groups that are often found near fjord-like bays in more southern areas, all the way to southeastern Alaska in the Gulf of Alaska. The blue king crab is only found in a few isolated areas, while the red king crab is found in many more places. This is likely because of changes in water temperature that happened after the last ice age, which limited the range of this cold-water-adapted species. Some of the things that might be directly limiting its range are its physiological needs for reproduction, competition with the red king crab, which is better adapted to warm water, being pushed out by warm-water predators, or the need for a place for larvae to settle down.