The Japanese spider crab is the largest arthropod on Earth with a massive reach.

Nature · Published 3 October 2026 Swipe more like this →

In short: With a leg span stretching nearly four meters, the Japanese spider crab is a true giant of the ocean floor. Despite its intimidating, spiky appearance and powerful claws, this deep-sea scavenger is known for a surprisingly gentle disposition and a unique habit of decorating its own shell for camouflage.

The Japanese spider crab, or taka-ashi-gani, is the only living member of the genus Macrocheira. Reaching up to 3.75 meters in leg span, it holds the record for the largest reach of any known arthropod. While its body width is modest at 40 centimeters, its total mass can hit 19 kilograms, making it the second-heaviest living arthropod after the American lobster. These crabs are found primarily off the southern coasts of Honshu, typically residing at depths between 50 and 600 meters.

These creatures are masters of disguise. Rather than seeking specific colors to match their surroundings, they actively adorn their bumpy carapaces with sponges and other organisms. By using their slender chelipeds to tear material from the substrate, they shape and attach these items to their shells through mechanical adhesion and natural secretions. This behavior helps them avoid predators while they are nocturnally active. Their life cycle is equally complex, involving four distinct larval stages that drift near the surface before the crabs eventually settle into the deeper, cooler waters of the ocean.

The species faces significant pressure from commercial fishing, particularly in Suruga Bay. Historical data shows a sharp decline in catch volumes, dropping from 24.7 tonnes in 1976 to 3.2 tonnes by 1985. To combat overfishing, Japan has implemented strict conservation measures, including a seasonal ban on harvesting during the mating months of January through April. These protections aim to allow populations to recover and provide juvenile crabs the necessary time to mature in their natural habitat.

Taxonomically, the crab remains a subject of study. Originally described by Coenraad Jacob Temminck in 1836, it was later placed in the genus Macrocheira. Some researchers suggest it may require its own unique family, as it shares primitive anatomical features with the genus Oncinopus, such as a mobile basal segment of the antennae. Whether viewed as a biological relic or a modern giant, the Japanese spider crab remains a fascinating example of evolutionary adaptation in the deep sea.

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