Japanese spider crab (Macrocheira kaempferi)

Classification (WoRMS)

Full classification as recorded by WoRMS: Kingdom: Animalia · Phylum: Arthropoda · Class: Malacostraca · Order: Decapoda · Family: Macrocheiridae · Genus: Macrocheira.

Accepted name: Macrocheira kaempferi · Authority: (Temminck, 1836) · Taxonomic status: accepted · AphiaID: 346131.

Synonyms and superseded combinations recorded for this taxon: Macrocheira ginzanensis Imaizumi, 1965; Macrocheira yabei (Imaizumi, 1957); Maja Kaempferi Temminck, 1836; Paratymolus yabei Imaizumi, 1957.

Source: World Register of Marine Species (WoRMS) — https://www.marinespecies.org/aphia.php?p=taxdetails&id=346131 (CC BY 4.0). Accessed 2026-09-23.

Biology and life history (SeaLifeBase)

Measured values published by SeaLifeBase for Macrocheira kaempferi. Only fields the database actually holds for this species are shown; these are database values, not aquarium guidance.

Maximum length: 30 cm · Depth range: 50–400 m · Habitat zone: benthic · Vulnerability index: 20 of 100 · Aquarium trade: never/rarely.

SeaLifeBase notes: Largest crab in the world. Leg span may measure up to 3.7 m and weight may exceed more than 13.6 kg (Ref. 99323).

Source: SeaLifeBase species summary (SpecCode 81340) — https://www.sealifebase.se/summary/Macrocheira-kaempferi.html (CC BY-NC 3.0 — non-commercial use only). Accessed 2026-09-23.

Distribution and occurrence records (GBIF)

26 georeferenced occurrence records for Macrocheira kaempferi are published through GBIF from 4 countries or marine areas. The map above plots 6 distinct locations from a sample of 26 records, omitting 9 inland records that carry an institution's coordinates rather than a collection site; it shows where the species has been observed and reported, not a modelled range.

Most records by country or area: Japan (21); China (3); Estonia (1); Chinese Taipei (1).

Source: GBIF Occurrence Search (taxonKey 5729749) — https://www.gbif.org/occurrence/search?taxon_key=5729749&has_coordinate=true (records CC0 / CC BY); WoRMS distribution records (MarineRegions) — https://www.marinespecies.org/aphia.php?p=taxdetails&id=346131 (CC BY 4.0); Natural Earth 110m basemap — https://www.naturalearthdata.com/ (public domain). Accessed 2026-09-23.

Description and natural history (Wikipedia)

The Japanese giant spider crab is the sole living member of the genus Macrocheira. Three fossil species of this genus are known: M. ginzanensis and M. yabei from the Miocene of Japan, and M. teglandi from the Oligocene. They are sought by crab fisheries, and are considered a delicacy in Japan. To prevent overexploitation from harming the species, conservation efforts have been put in place to protect them and their population from overfishing.

The Japanese giant spider crab is similar in appearance to the much smaller European spider crab (Maja squinado), though the latter, while within the same superfamily, belongs to a different family: the Majidae.

The Japanese spider crab has the greatest leg span of any known arthropod, reaching up to 3.7 m from claw to claw. The body may grow to 40 cm in carapace width and the whole crab can weigh up to 19 kg—second in mass only to the American lobster among all living arthropod species. The males have longer chelipeds; females have much shorter chelipeds, which are shorter than the following pair of legs.

Apart from its large size, the Japanese spider crab differs from other crabs in a number of ways. The first pleopods of males are unusually twisted, and the larvae appear primitive. The crab is orange with white spots along the legs. It is reported to have a gentle disposition despite its ferocious appearance. The Japanese spider crab also has a unique molting behavior that occurs for about 100 minutes, in which the crab loses its mobility, starts molting its carapace rear, and ends with molting its walking legs.

The Japanese spider crab has an armored exoskeleton that helps protect it from larger predators such as octopuses, but also uses camouflage. The crab's bumpy carapace blends into the rocky ocean floor. To further the deception, a spider crab adorns its shell with sponges and other animals. A spider crab is able to pick up and cover itself with such organisms by following a specific routine behavior. Upon picking up the object with the crab's slender chelipeds, the chelae are used to twist and tear off the organism, such as a worm tube or sponge, from the substrate on which it currently resides. Once the material is picked up, it is brought to the crab's mouthparts to orient and shape it before it is attached to the exoskeleton. Then, through mechanical adhesion and secretions, the materials attach to the crab, and are able to regenerate and colonize on the crab.

Unlike other species of crab, such as the Chilean crab Acanthonyx petiveri, the Japanese spider crab does not specifically look for matching colors to blend into its environment; it simply camouflages in a way that disguises its entire structure. This is most likely because Japanese spider crabs are nocturnally active, so instead of trying to disguise themselves when catching prey, they aim to avoid predators at night.

Japanese spider crabs are mostly found off the southern coasts of the Japanese island of Honshū, from Tokyo Bay to Kagoshima Prefecture. Outlying populations have been found in Iwate Prefecture and off Su-ao in Taiwan. Adults are found at depths between 50 and 600 m. They like to inhabit vents and holes in the deeper parts of the ocean. The temperature preference of adults is unknown, but the species is regular at a depth of 300 m in Suruga Bay, where the water generally is about 10 C. Based on results from public aquaria, Japanese spider crabs tolerate temperatures between 6 and 16 C, but are typically maintained at 10 - 13 C.

The Japanese spider crab is an omnivore, consuming both plant-matter and animals. It also sometimes acts as a scavenger, consuming dead/decaying fish. Some have been known to scrape the ocean floor for living plants and algae (such as kelp), while others pry open the shells of mollusks and small marine invertebrates.

Female crabs carry the fertilized eggs attached to their abdominal appendages until they hatch into tiny planktonic larvae. They can lay up to 1.5 million eggs per season, and these eggs hatch in 10 days on average. Once hatched, these larvae undergo four stages of development before they mature into adulthood.

The first, or prezoeal, stage lasts only a matter of minutes, with most molting within 15 minutes to enter the first zoeal stage. Prezoeal crabs have a small, transparent body.

M. kaempferi undergoes two zoeal stages and a megalopa stage before it reaches adulthood. Each of these stages is influenced greatly by temperature, both in terms of survival and stage length. The optimum rearing temperature for all larval stages is thought to be between 15 and 18 °C, with survival temperatures ranging from 11 to 20 °C. At these temperatures, the zoeal stages can last 7 to 18 days, with the megalopa stage lasting 25 to 45 days. Colder water is associated with longer durations in each stage.

During the larval stages, M. kaempferi is found near the surface, as the planktonic forms drift with ocean currents. This surface water ranges between 12 and 15 °C during the hatching season (January to March). This is much warmer than the waters at depths below 200 m, where adults are found, with waters steadily around 10 °C. Optimal temperatures have a 70% survival through the first zoeal stage, which is greatly reduced to a 30% survival in the second zoeal and megalopa stages.

The Japanese spider crab was originally described by Western science in 1836 by Coenraad Jacob Temminck under the name Maja kaempferi, based on material from Philipp Franz von Siebold collected near the artificial island Dejima. The specific epithet commemorates Engelbert Kaempfer, a German naturalist who lived in Japan from 1690 to 1692 and wrote about the country's natural history. It was moved to the genus Inachus by Wilhem de Haan in 1839, but placed in a new subgenus, Macrocheira. That subgenus was raised to the rank of the genus in 1886 by Edward J. Miers. Placed in the family Inachidae, M. kaempferi does not fit cleanly into that group, and it may be necessary to erect a new family just for the genus Macrocheira.

Source: Wikipedia: Japanese spider crab — https://en.wikipedia.org/wiki/Japanese_spider_crab (CC BY-SA 4.0). Accessed 2026-09-23.