Tradition: Japanese Mythology
Alternative Names: Akuta no Mushi; Akutamushi; Iron-Eating Insect
Category: Insect
The Myth
Akuta-mushi is a monstrous insect described in the Japanese text Shintō Yurai no Koto. It descended from the heavens during the reign of Emperor Yōmei (585–587), after the emperor expressed a desire to see a strange creature said to live in the sky and feed on iron. When the insect appeared, the emperor recognized it as the creature he had wished to see and ordered that it be kept and raised.
The insect fed on iron and grew to an enormous size, eventually becoming as large as a mountain. When iron was unavailable, it began devouring human beings instead. It also refused to obey the emperor’s commands, transforming from a remarkable creature into a threat to the imperial realm. The emperor ordered its destruction, but the insect’s body had become as hard as a mass of iron, rendering even swords useless against it.
As the people exhausted every possible means of defeating the monster, the sun goddess Amaterasu intervened. She submerged Akuta-mushi in a great river and finally destroyed it. According to the legend, the remains of its bones became gishaku, a magnetic stone obtained from the sea or other places and associated with the ability to attract iron.
The text survives in manuscripts dating to around the Muromachi period and presents Japanese myths within a worldview combining Shinto and Buddhist traditions. The story of Akuta-mushi appears in an explanation of the origins of Sakuku-no-Miya.
Although akuta-mushi resembles an old Japanese name for the cockroach, it is uncertain whether the creature in this story was intended to represent a real insect. Its tale follows a familiar pattern in which a ruler attempts to tame an extraordinary creature, only for it to grow uncontrollably powerful and turn against humanity. Similar stories describe the monstrous being known as Wazawai, whose iron-eating nature and magnetic remains also appear in the medieval Heike Monogatari tradition.
Sources
“Akuta-mushi.” 新版TYZ 妖怪図鑑 (New TYZ Yokai Encyclopedia). https://tyz-yokai.blog.jp/archives/1075890032.html