Crustaceans
Japanese spider crab
Macrocheira kaempferi
Epipelagic zone · Mesopelagic zone
With legs that can span nearly four meters, this deep-sea Japanese crab holds the record for the largest living arthropod on Earth.
🗺️ Geographic range
Endemic to the deep waters around Japan, mainly along the Pacific coast of Honshu and Kyushu (Sagami, Suruga, and Tosa bays, the Kii Peninsula), with a few records as far south as Taiwan.
📊 Population
Not formally assessed by the IUCN due to insufficient global data; in Japan, where it is fished as a delicacy, a regulated seasonal fishery (closed during spawning, with minimum catch-size rules) aims to prevent overexploitation within its very limited range.
Habitat
- Pacific Ocean · High seas / open water · Mesopelagic zone · Permanent
🥚 Reproduction
The female lays up to 1.5 million eggs between January and April, producing larvae that pass through several stages (zoea, then megalopa) before reaching adult form.
Behaviour
- Diet
- An opportunistic scavenger and detritivore, it feeds on dead fish, decaying organic matter, and slow-moving invertebrates, playing a key role in deep-sea nutrient recycling.
- Hunting
- A scavenger rather than an active hunter, it also captures slow-moving or already weakened invertebrates when the opportunity arises.
- Communication
- No known vocalizations; communication is mainly chemical and tactile via the antennae.
- Social life
- Generally solitary and slow-moving, it migrates to shallower water (around 50 m) during the breeding season.
Physiology
- Anatomy
- Its relatively small body (up to 40 cm wide) contrasts sharply with its enormous legs, which can span nearly 4 meters — an absolute record among arthropods.
- Respiration
- Gill-based, with gills protected beneath the carapace.
- Vision
- Compound eyes on mobile stalks, adapted to the dim light of deep water.
- Adaptations
- Like all crustaceans, it grows through successive molts, each one a moment of high vulnerability while its shell remains soft.
⚡ Its extraordinary abilities
- The largest leg-span of any arthropod on Earth, nearly 4 meters
- An exceptional lifespan that may reach a century — rare among crustaceans
🏆 Records
Largest living arthropod on Earth
With a leg-span that can approach 4 meters, no other known arthropod, on land or at sea, matches it in span.
If you cross paths with this animal…
Risk: Its powerful claws can deliver a painful pinch if handled, but the animal itself is not aggressive.
Behaviour: Slow and unobtrusive, it normally lives at depths far from human interaction, except in aquariums or during fishing.
Advice: If observed or handled (aquarium, fishing), avoid the claws and support it by the body.
💡 Did you know?
- Its leg-span is the largest of any arthropod alive, exceeding even some giant fossil insects.
- Considered a delicacy in Japan, it is subject to a strictly regulated seasonal fishery to prevent overexploitation.
