QuestionJapanese spider crab
What Is the Biggest Crab in the World? Japanese Spider Crab
The biggest crab in the world is the Japanese spider crab (Macrocheira kaempferi). Its legs can span about 3.7 m (12 ft) from claw tip to claw tip, the widest reach of any arthropod, and it weighs up to about 19 kg (42 lb), more than any other crab. It lives in deep water off the Pacific coast of Japan.
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The Japanese spider crab: record leg span
The Japanese spider crab is a giant mainly because of its legs. Measured with the claws and legs stretched out, the largest crabs span about 3.7 m (12 ft), wider than a small car is long. The shell itself is only up to about 40 cm (16 in) across, so the crab looks like a modest body suspended in a frame of long, thin stilts.
Most Japanese spider crabs are much smaller than the record holders. Those caught by fishers in Suruga Bay typically span about 1–1.2 m (3.3–3.9 ft). The giants live on the seafloor 50–600 m (160–1,970 ft) deep, where cold, calm water supports their spindly legs.
How a crab is “biggest” depends on what you measure. Leg span, shell width and weight each give a slightly different ranking.
The largest crabs compared
| Crab | Leg span | Shell width | Maximum weight | Where it lives |
|---|---|---|---|---|
| Japanese spider crab | Up to about 3.7 m (12 ft) | Up to about 40 cm (16 in) | About 19 kg (42 lb) | Deep water off Japan |
| Tasmanian giant crab | Much shorter legs | Up to about 46 cm (18 in) | About 17.6 kg (39 lb) reported | Deep water off southern Australia |
| Red king crab | Up to about 1.5–1.8 m (5–6 ft) | Up to about 28 cm (11 in) | About 11–12.7 kg (24–28 lb) | North Pacific; introduced to the Barents Sea |
| Coconut crab | About 0.9 m (3 ft) | Body up to about 40 cm (16 in) long | About 4.1 kg (9 lb) | Tropical Indian and Pacific Ocean islands |
| Edible crab | Short legs | Up to about 25 cm (10 in) | About 3 kg (6.6 lb) | Northeastern Atlantic and North Sea |
| Atlantic blue crab | Short legs | Up to about 23 cm (9 in) | About 0.5 kg (1.1 lb) | Western Atlantic; introduced to Europe |
Maximum figures come from exceptional individuals; typical adults of every species are smaller. The Atlantic blue crab, one of the best-known crabs in North America, is included for scale.
Tasmanian giant crab: the widest shell
The Tasmanian giant crab (Pseudocarcinus gigas) lives on rocky and muddy bottoms off southern Australia, usually 110–400 m (360–1,310 ft) deep. Its shell can reach about 46 cm (18 in) across, wider than the Japanese spider crab’s, and large males have been reported at about 17.6 kg (39 lb). By body bulk, it is the main rival to the Japanese giant.
Males grow more than twice as big as females, which do not exceed about 7 kg (15 lb). A big male has one enormous claw, which can be longer than its shell is wide. The species grows very slowly in cold water: large females may go many years between molts, which makes it easy to overfish.
King crabs and the coconut crab: big, but not true crabs
Two famous giants look like crabs but belong to a different branch of the crustacean family tree. King crabs and coconut crabs are anomurans, relatives of hermit crabs that evolved a crab-like body on their own. A quick way to tell: they seem to have only three pairs of walking legs behind the claws, because the last pair is tiny and tucked away.
The red king crab (Paralithodes camtschaticus) is the largest king crab. NOAA Fisheries gives a maximum of about 11 kg (24 lb) and a leg span of about 1.5 m (5 ft), and the largest reported crabs reach about 12.7 kg (28 lb) and 1.8 m (5.9 ft). It lives in cold water from the Bering Sea and Gulf of Alaska to Japan, and Soviet scientists introduced it to the Barents Sea in the 1960s. It is now common off northern Norway, making it Europe’s biggest crab-like animal.
The coconut crab (Birgus latro) is the largest arthropod that lives on land. It can weigh up to about 4.1 kg (9 lb) and span about 0.9 m (3 ft) across its legs. Adults breathe air and will drown if kept underwater for long. The IUCN lists the coconut crab as Vulnerable, because it has disappeared from many inhabited islands.
Is the Japanese spider crab the largest arthropod?
By leg span, yes. No other living arthropod, a group that includes insects, spiders, centipedes and crustaceans, reaches as far. By weight, however, the record goes to a lobster: an American lobster caught off Nova Scotia in 1977 weighed 20.1 kg (44.4 lb), slightly more than the heaviest Japanese spider crabs. That record is explained in how big do lobsters get? and the two groups are compared in crab vs lobster.
Some extinct arthropods were even bigger. Fossil sea scorpions such as Jaekelopterus, which lived about 390 million years ago, are estimated to have reached about 2.5 m (8 ft) in body length, and the giant millipede relative Arthropleura was of similar length. Today’s largest animals are ranked in the largest animals in the world.
Why do some crabs grow so big?
Most giant crabs live in cold, deep water, and scientists think that is no coincidence. Cold water holds more oxygen, and animals that grow slowly in cold conditions often reach larger sizes and live longer than their warm-water relatives. Water also supports an animal’s weight, so long legs that would buckle on land can carry a crab across the seafloor.
The coconut crab is the exception that proves the rule: on land, even the largest arthropod weighs only about 4 kg (9 lb). Without water to hold them up, a heavy outer skeleton and the need to molt it put a firm limit on size.
Frequently asked questions
What is the biggest crab ever recorded?
The largest crabs on record are Japanese spider crabs with a leg span of about 3.7 m (12 ft) from claw tip to claw tip and a weight of up to about 19 kg (42 lb). Published figures vary slightly, because a crab's legs are hard to measure exactly.
What is the biggest crab in the United States?
The red king crab of Alaska is the biggest. NOAA Fisheries says it can reach about 11 kg (24 lb) with a leg span of about 1.5 m (5 ft), and some sources report up to 12.7 kg (28 lb). Most crabs caught today are much smaller, around 3 kg (6–7 lb).
What is the biggest crab in Europe?
The red king crab, which the Soviet Union introduced to the Barents Sea in the 1960s and which now lives off northern Norway and Russia. Among native European species, the edible crab is the heaviest common crab, with a shell up to about 25 cm (10 in) wide and a weight of up to about 3 kg (6.6 lb).
What is the biggest land crab?
The coconut crab of tropical Indian and Pacific Ocean islands. It can weigh up to about 4.1 kg (9 lb) and span about 0.9 m (3 ft) across its legs, making it the largest arthropod that lives on land.
Is a king crab bigger than a Japanese spider crab?
No. The red king crab, the largest king crab, reaches about 1.5–1.8 m (5–6 ft) across its legs and 11–12.7 kg (24–28 lb), while the Japanese spider crab reaches about 3.7 m (12 ft) and 19 kg (42 lb).
How big is a Japanese spider crab's body?
Much smaller than its legs suggest. The shell is up to about 40 cm (16 in) across, roughly the size of a large serving platter, and most of the crab's span comes from its long, thin legs.
Sources and further reading
- Encyclopaedia Britannica, "Spider crab"
- NOAA Fisheries, "Red King Crab"
- IUCN Red List of Threatened Species, "Birgus latro"
- World Register of Marine Species (WoRMS), "Pseudocarcinus gigas"
Cite this page
“What Is the Biggest Crab in the World? Japanese Spider Crab.” Animal Atlas, https://animals.bigworldlist.com/questions/what-is-the-biggest-crab-in-the-world/.
