Heikegani is a species of crab native to Japan, with a shell that bears a pattern resembling a human face. According to Japanese folklore, the Heikegani crabs contain the souls of the Heike samurai warriors who were slain at the Battle of Dan-no-ura in 1185 AD, a war over the Japanese imperial throne. The story goes that the Heike samurai, reincarnated into the Heikegani (Heikeposis japonica) crab, were showing their allegiance to their clan by donning a fierce mask on their shells. The battle of Dan-no-ura (Dannoura), immortalized in the Heike Monogatari (the Tale of Heike,) was a pivotal moment in Japan’s history, which established the first shogunate (military dictatorship) and resulted in the death of a child emperor.

The Heikegani Crab (Heikeopsis japonica) and a stylize Kabuki samurai face. Image source .

The Battle of Dan-no-ura

The Battle of Dan-no-ura was preceded by an immense struggle between the imperial rulers of Japan, the Taira clan (later known as Heike), who the Heikegani crabs are named after, and the Minamoto clan (Genji), who were fighting for control of the throne at the end of the 12th century in the Genpei War (1180-1185).

On 24 the April, 1185 AD, the two powerful Samurai clans fought to the death on the Dan-no-ura bay of Japan’s Inland Sea. The ruling Taira clan (Heike), was led by their child-Emperor, Antoku, and his grandmother. The Heike had ruled for many decades, but now, massively outnumbered, they faced defeat at the hands of the Minamoto.

During the battle, a member of the royal household took the seven-year-old Emperor Antoku and plunged with him into the water in the Shimonoseki Straits, drowning the child emperor, rather than allowing him to be captured by the opposing forces. His mother and grandmother followed him in their grief. Antoku came to be worshipped as Mizu-no-kami ("god of water”).

This crucial battle was a cultural and political turning point in Japanese history: Minamoto Yoritomo became the first Shogun, or military ruler, of Japan. Dan-no-ura marked the beginning of seven centuries, in which Japan was ruled by warriors and Shoguns instead of Emperors and aristocrats.

Dan-no-ura tatakai no zu (‘Battle of Dannoura’). The Heikegani crabs can be seen in the lower half of the painting. Image source .

The Fate of the Heike Samurai

For the Heike samurai, surrender to the enemy was never an option. Those that were not slain in battle, committed suicide by drowning themselves along with their emperor. Their bodies became food for the heikegani crabs who lay in wait on the sea floor.

According to the Japanese legend, the ghosts or souls of the Heike samurais were reincarnated into the Heikegani crabs who ate their remains, their angry faces now shown on the shells of the crabs. To this day, it is said that the Heikegani crabs roam the depths of the oceans around Japan, searching for the lost heirlooms of their empire.

Defeated Heike warriors are turned into crabs as they are tossed from their ships. Painting by Kuniyoshi. Image source .

Carl Sagan’s Theory of Artificial Selection

During an episode of the PBS science show, ‘Cosmos: A Personal Voyage’, Carl Sagon expounded on a theory put forward by Julian Huxley in 1952, to explain the strange face-like characteristics of the Heikegani crab shell. Huxley theorized that the crab’s samurai faces are the result of artificial selection. He proposed the fishermen fishing Japan’s waters would throw back any crabs whose shells looked like a samurai’s face out of respect for the fallen heike. This preserved the DNA of the heikegani with samurai-like faces while thinning the genetic lines of those without.

The problem with this theory is that the Heikegani crabs, which have a maximum length of 1.2 inches, are too small to be eaten, so it is unlikely they were ever caught for food in the first place. Furthermore, analysis of the shells has shown that the face-like patterns are simply the result of connection points for muscle and ligament tissue. Finally, Heikegani crabs are not the only crabs with a human-looking face on the shell. A variety of crabs from the family Dorippidae all appear to have human faces on their backs.

A far more plausible theory is that any resemblance of a human face seen in the shells of the Heikegani crabs is the result of pareidolia, the human brain’s innate ability to recognize faces and human forms in a set of random stimuli. Common examples include seeing images of animals or faces in clouds, the Virgin Mary on toast, and the man in the moon.

Pareidolia is the brain’s innate ability to see faces in a set of random stimuli.

The Heikegani crab has inspired reverence to ancient legends, as well as scientific investigation into the power of selection. While many believe the angry samurai face in the crab’s shell is simply the result of the psychological phenomenon of pareidolia, others believe that the grimaced faces are the Heike samurai warriors, who were reborn and are still, somehow, watching over them.

Watch segment from ‘Cosmos: A Personal Voyage’ about the legend of the Heikegani crabs:

Featured image: ‘The Ghost of Taira Tomomori’ by Utagawa Kuniyoshi – depicts The ghost of Taira Tomomori along with the anchor he drowned with, and heikegani with faces of fallen soldiers. Image source .

References

The Samurai Crab. Martin, J.W. 1993. Terra, 31:4, 30-34.

Heikegani: The Samurai Ghost Crab – Introvert Japan

The Heikegani Crabs and the Problem with Pareidolia – Martin J Clemens

Heikegani: The Samurai Crab – Japan Powered

Samurai Crabs: Transmogrified Japanese warriors, the product of artificial selection, or pareidolia? - Arthropoda