Crab Spider

Verified Timeline

Lore & Background

The Japanese giant 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. Four species of the genus Macrocheira are known from fossils: Macrocheira sp. from the Pliocene Takanabe Formation in Japan, M. ginzanensis and M. yabei from the Miocene of Japan, and M. teglandi from the Oligocene east of Twin River, Washington, United States. The genus is similar in anatomical arrangement to the genus Oncinopus, seeming to preserve the earliest stage of anatomical evolution in the family Inachidae.

In Their Own Story

The Japanese giant 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.

Reader's Guide

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 (160 and 1,970 ft). 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 metres (980 ft) in Suruga Bay, where the water generally is about 10 °C (50 °F). Based on results from public aquaria, Japanese spider crabs tolerate temperatures between 6 and 16 °C (43 and 61 °F), but are typically maintained at 10–13 °C (50–55 °F). 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. 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. In total, 24.7 tonnes (54,000 lb) were collected in 1976, but fell to only 3.2 tonnes (7,100 lb) in 1985. The fishery is centred on Suruga Bay. The crabs are typically caught using small trawling nets.

Did You Know?

• The Japanese giant spider crab has the greatest leg span of any known arthropod, reaching up to 3.7 m (12.1 ft) from claw to claw.
• The body may grow to 40 cm (16 in) in carapace width and the whole crab can weigh up to 19 kg (42 lb)—second in mass only to the American lobster among all living arthropod species.
• Female crabs can lay up to 1.5 million eggs per season, and these eggs hatch in 10 days on average.
• The Japanese name for this species is taka-ashi-gani, literally translating to 'tall-legged crab'.
• The specific epithet kaempferi commemorates Engelbert Kaempfer, a German naturalist who lived in Japan from 1690 to 1692.