Animal Diversity Web

Ge­o­graphic Range

The Japan­ese spi­der crab Macrocheira kaempferi is mostly lim­ited to the Pa­cific side of the Japan­ese is­lands, Kon­shu and Kyushu, usu­ally at a lat­i­tude be­tween 30 and 40 de­grees North. They are found most often in the Sagami, Su­ruga, and Tosa bays, as well as off the coast of the Kii penin­sula. How­ever, the crab has been found as far south as Su-ao, in East­ern Tai­wan. This is most likely a one time event; it is pos­si­ble a fish­ing trawler or ex­treme weather may have car­ried this in­di­vid­ual much fur­ther south than its home range. (Huang, et al., 1990; Okamoto, 1993; Okamoto, 2001; Park, 1988; Sakai, 2010)

• Biogeographic Regions
• palearctic
  • native

Habi­tat

Japan­ese spi­der crabs most often in­habit the sandy and rocky bot­tom of the con­ti­nen­tal shelf and slope at an av­er­age depth of 150-300 me­ters. They have, how­ever been found at depths of 600 feet. Dur­ing spawn­ing sea­son the crabs spend most of their time in shal­lower wa­ters around 50 me­ters. In Su­ruga Bay, at depths of 300 me­ters, the tem­per­a­ture is around 10 de­grees Cel­sius. Younger crabs tend to live in shal­lower areas with warmer tem­per­a­tures. (Okamoto, 1993; Sakai, 2010)

• Habitat Regions
• temperate
• saltwater or marine

• Aquatic Biomes
• benthic
• coastal

• Range depth

  50 to 600 m

  164.04 to 1968.50 ft

• Average depth

  200 m

  656.17 ft

Phys­i­cal De­scrip­tion

Al­though not the heav­i­est, the Japan­ese giant spi­der crab is the largest known liv­ing arthro­pod. The well-cal­ci­fied cara­pace is only around 37 cen­time­ters long, but adult spec­i­mens can be nearly 4 me­ters long from one tip of one che­liped (a claw-bear­ing leg) to the other when stretched apart. The cara­pace of Macrocheira kaempferi is sub-cir­cu­lar and pear-shaped (pyri­form), nar­rower to­wards the head. Fe­males tend to have wider, al­though slightly smaller, ab­domens than males. Spiny and stubby tu­ber­cles (growths) cover the cara­pace, which ranges from dark or­ange to light tan in color. It pos­sesses no cryp­tic col­oration and is un­able to change color. The ros­trum (an ex­ten­sion of the cara­pace above the head) is shaped into two slen­der spines that jut out from be­tween the eyes. The base of the well-de­vel­oped an­ten­nae is fused with the epis­tome (the area above the mouth).

The cara­pace tends to stay the same size through­out adult­hood, but the walk­ing legs and che­lipeds lengthen con­sid­er­ably as the crab ages. Spi­der crabs are known for hav­ing long, spindly legs. Like the cara­pace, the legs are also or­ange, but may be blotchy and mot­tled with both or­ange and white. The walk­ing legs of Macrocheira kaempferi end sim­ply in in­wardly-curv­ing dactyls (the mov­able part at the tip of a walk­ing leg). These as­sist the crea­ture in climb­ing and hook­ing onto rock, but pre­vent it from pick­ing up or grasp­ing ob­jects. In adult males the che­lipeds are far longer than any of the walk­ing legs, with the right and left che­lipeds being of equal size. Fe­males, on the other hand, tend to pos­sess che­lipeds that are shorter than the other walk­ing legs. The merus (upper por­tion of the leg) is slightly longer than the palm (por­tion of the leg con­tain­ing the un­mov­ing part of the claw), but com­pa­ra­ble in shape. The weak mov­able fin­ger is small, tak­ing up less than a quar­ter of the palm. Al­though long, the legs are often weak. One study re­ported that nearly three quar­ters of these crabs are miss­ing at least one limb, most often one of the first walk­ing legs. This is be­cause the limbs are long and poorly-jointed to the body of the or­gan­ism, and tend to come off due to preda­tors and nets. Spi­der crabs can usu­ally sur­vive with up to 3 walk­ing legs miss­ing. The walk­ing legs often grow back dur­ing the suc­ces­sive molts. (En­cy­clopae­dia Bri­tan­nica On­line, 2011; Okamoto, 2001; Park, 1988; Sakai, 1965; Sakai, 2010; Wick­sten, 1992)

• Other Physical Features
• ectothermic
• heterothermic
• bilateral symmetry

• Sexual Dimorphism
• sexes shaped differently

• Range mass

  16 to 20 kg

  35.24 to 44.05 lb

• Range length

  3.7 (high) m

  12.14 (high) ft

• Average length

  3 m

  9.84 ft

De­vel­op­ment

This species goes through two zoeal stages and one mega­lopa stage. The zoeal stages gen­er­ally last be­tween 12-37 days, a shorter du­ra­tion than other crabs in the same re­gion. The mega­lopa stage typ­i­cally lasts an av­er­age of 30 days. Dur­ing the first molt (the pre­zoeal stage) the hatch­lings writhe about, even­tu­ally slowly drift­ing to the sea bed. Here, each hatch­ling thrashes about until it flicks up the spines on its cara­pace. This dis­lodges the cu­ti­cle, and al­lows it to wrig­gle out by twist­ing and pulling until it frees it­self. (Clark and Web­ber, 1991; Okamoto, 1991; Okamoto, 1993; Okamoto, 2001; Okamoto, 2003)

The op­ti­mal rear­ing tem­per­a­ture for all lar­val stages is be­tween 15-18 de­grees Cel­sius, while the sur­vival tem­per­a­ture is 11-20 de­grees Cel­sius. Lar­val stages can most likely be found at shal­lower depths, then later move to deeper wa­ters. In Su­ruga Bay, the tem­per­a­ture at 300 me­ters is around 10 de­grees, and only adults may be found at these depths. These sur­vival tem­per­a­tures are much higher than those of other de­ca­pod species in the re­gion. In the lab, at op­ti­mum growth con­di­tions, only around 75% sur­vive the first zoeal stage. This num­ber drops to around 33% for the sec­ond zoeal and mega­lopa stages. (Okamoto, 1993)

• Development - Life Cycle
• metamorphosis

Re­pro­duc­tion

These spi­der crabs mate sea­son­ally dur­ing early spring, from Jan­u­ary through March. Mat­ing be­hav­ior is rarely ob­served. Male crabs hold sperm in sper­matophores, which are in­serted into the fe­male's ab­domen using the first two che­lipeds. (Arakawa, 1964; Hart­noll, 1969)

Even though ju­ve­nile stages are well-doc­u­mented in lab­o­ra­to­ries, re­pro­duc­tion in­for­ma­tion con­cern­ing M. kaempferi in its nat­ural habi­tat is sparse. Fer­til­iza­tion is in­ter­nal. A fe­male often lays up to 1.5 mil­lion eggs per sea­son, but only a few sur­vive. Eggs are around 0.63-0.85 mm in di­am­e­ter. The hatch­ing du­ra­tion is around 10 days. The breed­ing du­ra­tion is around one year, al­though exact times are not avail­able. (Arakawa, 1964; Hart­noll, 1969; Okamoto, 1993)

• Key Reproductive Features
• seasonal breeding
• gonochoric/gonochoristic/dioecious (sexes separate)
• sexual
• fertilization
  • internal
• oviparous

• Breeding interval

  Giant Japanese spider crabs mate once a year, seasonally between January and April

• Breeding season

  Early spring

• Range number of offspring

  1,500,000 eggs (high)

Fe­males carry eggs on their backs and lower bod­ies dur­ing in­cu­ba­tion until they hatch. In this way, the mother can stir the water with her back legs to oxy­genate the eggs. After the eggs hatch, there is no parental in­vest­ment and the lar­vae are left to fend for them­selves. (Arakawa, 1964; Hart­noll, 1969)

• Parental Investment
• female parental care
• pre-hatching/birth
  • protecting
    • female

Lifes­pan/Longevity

Rel­a­tively lit­tle is known in­for­ma­tion re­gard­ing the longevity of this species. It is often re­ported that one of these crabs may live to be 100 years old in its nat­ural habi­tat, but this may be con­jec­ture. Other re­ports in­di­cate that M. kaempferi gen­er­ally live for over half of a cen­tury. (; Park, 1988)

• Typical lifespan
  Status: wild

  100 (high) years

Be­hav­ior

Macrocheira kaempferi crabs are very placid crea­tures, spend­ing much of its days search­ing for food. These crabs roam the seafloor but are not able to swim. Al­though many spi­der crabs dec­o­rate them­selves, using their chelae (claws) to tear up ob­jects and at­tach them to the hooked barbs on their ros­trum and cara­pace. Adult Japan­ese spi­der crabs do not. How­ever, Macrocheira kaempferi is large enough that it has few preda­tors, and lives deep enough that there are few ob­jects to use for dec­o­ra­tion. (Park, 1988; Wick­sten, 1992)

• Key Behaviors
• motile
• migratory
• solitary

Home Range

There is no in­for­ma­tion avail­able con­cern­ing the home range for this species.

Com­mu­ni­ca­tion and Per­cep­tion

Not much is known about com­mu­ni­ca­tion in Macrocheira kaempferi. They often scav­enge for food alone, and there is lit­tle com­mu­ni­ca­tion be­tween mem­bers of the species, even when iso­lated with other spi­der crabs in aquaria. The an­ten­nae are greatly re­duced. The eye­stalks are also short and stubby. Be­cause these crabs are not ac­tive hunters and do not have many preda­tors, their sen­sory sys­tems are not as acute as those of many other de­capods in the same area. (Huang, et al., 1990; Park, 1988)

• Communication Channels
• visual

• Perception Channels
• visual
• tactile

Food Habits

Macrocheira kaempferi is an om­niv­o­rous scav­enger. These large crus­taceans gen­er­ally do not hunt, but in­stead crawl along and pick at dead and de­cay­ing mat­ter along the sea bed. This in­cludes both an­i­mal and plant mat­ter. They oc­ca­sion­ally eat liv­ing kelp and algae. Al­though they move slowly, giant crabs oc­ca­sion­ally hunt for small ma­rine in­ver­te­brates that they can catch eas­ily. Mariners used to tell tales of M. kaempferi drag­ging sailors un­der­wa­ter and feast­ing on their flesh. This is gen­er­ally re­garded as un­true, al­though it is cer­tainly plau­si­ble that one of these crabs would feast upon the dead body of a sailor who had pre­vi­ously drowned. (En­cy­clopae­dia Bri­tan­nica On­line, 2011; Sakai, 1965; Ueda, et al., 1989)

• Primary Diet
• omnivore
• detritivore

• Animal Foods
• fish
• carrion
• aquatic crustaceans
• other marine invertebrates

• Plant Foods
• algae
• macroalgae

• Other Foods
• detritus

Pre­da­tion

Many ju­ve­niles dec­o­rate their shells with sponges, kelp, or other ob­jects to dis­guise them­selves. How­ever, most adults do not be­cause their large size de­ters most preda­tors. Al­though slow-mov­ing, they use their claws against smaller preda­tors. (Wick­sten, 1992)

• Anti-predator Adaptations
• cryptic

Ecosys­tem Roles

Macrocheira kaempferi is not an ac­tive preda­tor, as it mainly scav­enges the seafloor for dead and de­cay­ing mat­ter.

While nearly all spi­der crabs tend to dec­o­rate their cara­paces with sponges and other items, M. kaempferi does it less than oth­ers be­cause it has so few preda­tors and there­fore no need for cam­ou­flage. Sponges pro­vide cam­ou­flage and pro­tec­tion for the crab; the spi­der crab car­ries the sponge to new areas and pos­si­bly pro­vides it with drift­ing food. (; Sakai, 2010; Wick­sten, 1992)

Eco­nomic Im­por­tance for Hu­mans: Pos­i­tive

Macrocheira kaempferi is quite use­ful and im­por­tant to the Japan­ese cul­ture. The crabs are often served as a del­i­cacy dur­ing the ap­pro­pri­ate crab-fish­ing sea­sons and are eaten both raw and cooked. Be­cause the walk­ing legs are so long, re­searchers often use ten­dons from the legs or che­lipeds. In some parts of Japan, it is pop­u­lar to take and dec­o­rate the cara­pace. Macrocheira kaempferi is also com­mon in aquaria be­cause of its gen­tle dis­po­si­tion. (Free­man, 2010; Ya­m­aguchi, et al., 2003)

• Positive Impacts
• food
• body parts are source of valuable material
• research and education

Eco­nomic Im­por­tance for Hu­mans: Neg­a­tive

There are no known ad­verse ef­fects of Macrocheira kaempferi on hu­mans. They rarely come into con­tact with hu­mans, and their weak claws are fairly harm­less.

Con­ser­va­tion Sta­tus

There is in­suf­fi­cient data con­cern­ing the con­ser­va­tion sta­tus for the Japan­ese spi­der crab. The catch of this species has de­clined con­sid­er­ably in the last 40 years. Some re­searchers have put forth a method for re­cov­ery which in­volves re­stock­ing with ju­ve­nile crabs ar­ti­fi­cially cul­tured in fish­eries. In Japan, laws pro­hibit fish­er­men from catch­ing M. kaempferi dur­ing mat­ing sea­son in the early spring, from Jan­u­ary until April, in order to keep nat­ural pop­u­la­tions up and to give the species a chance to spawn. (Free­man, 2010; Okamoto, 1993)

• IUCN Red List

  Not Evaluated

• US Federal List

  No special status

• CITES

  No special status

• State of Michigan List

  No special status

Other Com­ments

There has been much con­flict be­tween lar­val- and adult- based clas­si­fi­ca­tion. Some sup­port the use of a sep­a­rate fam­ily for this species, but much fur­ther study is needed. (Clark and Web­ber, 1991; Ng, et al., 2008)

Orig­i­nally M. kaempferi was in­cor­rectly placed in the genus Maja be­fore later being placed in Macrocheira. Today, this species is the only known sur­viv­ing mem­ber of Macrocheira, and is re­garded as one of the ear­li­est-branch­ing mem­bers of Ma­ji­dae. For this rea­son, it is often re­ferred to as a liv­ing fos­sil. (Clark and Web­ber, 1991; Ng, et al., 2008)

Con­trib­u­tors

William Riebel (au­thor), Uni­ver­sity of Michi­gan-Ann Arbor, Phil Myers (ed­i­tor), Uni­ver­sity of Michi­gan-Ann Arbor, Renee Mul­crone (ed­i­tor), Spe­cial Pro­jects.

Ref­er­ences

Arakawa, K. 1964. On mat­ing be­hav­ior of the giant Japan­ese crab, Macrocheira kaempferi. Re­searches on Crus­tacea, 1: 41-46.

Clark, P., W. Web­ber. 1991. A re­descrip­tion of Macrocheira kaempferi (Tem­minck, 1836) zoeas with a dis­cus­sion of the clas­si­fi­ca­tion of the Ma­joidea Samouelle, 1819 (Crus­tacea: Brachyura). Jour­nal of Nat­ural His­tory, 25 (5): 1259-1279.

En­cy­clopae­dia Bri­tan­nica On­line, 2011. "Giant Crab" (On-line). Ac­cessed May 02, 2011 at http://​www.​britannica.​com/​EBchecked/​topic/​232976/​giant-crab?​cameFromBol=true.

Free­man, S. 2010. ""Crabzilla": The biggest crab ever seen in Britain...​and it's still grow­ing" (On-line). Mail On­line. Ac­cessed May 02, 2011 at http://​www.​dailymail.​co.​uk/​news/​article-1250168/​Biggest-crab-seen-Britain.​html.

Hart­noll, R. 1969. Mat­ing in the Brachyura. Crus­taceana, 16 (2): 161-181.

Hiro, F. 1938. Notes on the an­i­mals found on Macrocheira kaempferi de Haan I. Cir­ripeds, II. Mol­luscs. An­no­ta­tions Zo­o­log­i­cae Japo­nenses, 17: 465-471.

Huang, J., H. Yu, M. Takeda. 1990. Oc­curence of the giant spi­der crab, Macrocheira kaempferi (Tem­mink, 1836) (Crus­tacea, De­capoda, Ma­ji­dae) in Tawi­wan. Bul­letin of the In­sti­tute of Zo­ol­ogy, Acad­e­mia Sinica, 29 (3): 207-212.

Ng, P., D. Guinot, P. Davie. 2008. Sys­tema Brachyuro­rum: Part I. An An­no­tated Check­list of Ex­tant Brachyu­ran Crabs of the World. The Raf­fles Bul­letin of Zo­ol­ogy, 17: 99.

Okamoto, K. 1993. In­flu­ence of tem­per­a­ture on sur­vival and growth of lar­vae of the giant spi­der crab Macrocheira kaempferi (Crus­tacea, De­capoda, Ma­ji­dae). Bul­letin of the Japan­ese So­ci­ety of Sci­en­tific Fish­eries, 59 (3): 419-424.

Okamoto, K. 2001. Limb loss in the giant spi­der crab Macrocheira kaempferi. Bul­letin of the Shizuoka Pre­fec­tural Fish­eries Ex­per­i­ment Sta­tion, 36: 25-27.

Okamoto, K. 1991. On the de­vel­op­ment, hatch and cul­ture of eggs of giant spi­der crab, Macrocheira kaempferi. Bul­letin of the Shizuoka Pre­fec­tural Fish­eries Ex­per­i­ment Sta­tion, 26: 21-33.

Okamoto, K. 2003. Stud­ies on the lar­val rear­ing of the giant spi­der crab, Macrocheira kaempferi-VII The ef­fect of an­tibi­otics on sur­vival and growth of lar­vae. Bul­letin of the Shizuoka Pre­fec­tural Fish­eries Ex­per­i­ment Sta­tion, 38: 37-41.

Park, E. 1988. Around the mall and be­yond: Jape­nese spi­der crabs at the in­ver­te­brate ex­hibit at the na­tional zoo. Smith­son­ian, 19: 18.

Sakai, K. 2010. "Macrocheira kaempferi" (On-line). Ma­rine Species Iden­ti­fi­ca­tion Por­tal. Ac­cessed May 02, 2011 at http://​species-identification.​org/​species.​php?​species_​group=crabs_​of_​japan&​id=857&​menuentry=soorten.

Sakai, T. 1965. The Crabs of Sagami Bay. Hon­olulu: East-West Cen­ter Press.

Ueda, R., T. Ya­suhara, H. Sugita, Y. Deguchi. 1989. Gut mi­croflora of the Japan­ese giant crab Macrocheira kaempferi. Bul­letin of the Japan­ese So­ci­ety of Sci­en­tific Fish­eries, 55: 181.

Wick­sten, M. 1992. A re­view and a model of dec­o­rat­ing be­hav­ior in spi­der crabs (De­capoda, Brachyura, Ma­ji­dae). Crus­taceana, 64 (3): 314-325.

Ya­m­aguchi, I., S. Itoh, M. Suzuki, M. Sakane, A. Osaka, J. Tanaka. 2003. The chi­tosan pre­pared from crab ten­don I: the char­ac­ter­i­za­tion and the me­chan­i­cal prop­er­ties. Bio­ma­te­ri­als, 24 (12): 2031-2036.