Giant earthworms have been reported all over Japan, mostly in southwestern Honshu, with some described as being 20 feet long. The largest known earthworm species in Japan, the siebold worm, has unusually large specimens reaching 25 centimetres (10 in). The giant worms aren’t just longer, but thicker as well. Siebold worms are also bright blue, unlike the giant worm reports, which are described as looking like regular earthworms, just scaled up in size.
The first report of a giant worm in Japan was in 1712 in the Tamba Province, now Hyogo. The account described a large landslide that occurred in a village. In the debris of the landslide, farmers found two gigantic earthworms, one five feet long, the other ten feet long. Another landslide that occurred in the same general vicinity allegedly unearthed a 15-foot long worm. In Mikata-Gun in the mountains of Hyogo, a farmer found a 3.3 foot long, two cm thick earthworm while planting a tree.
In Okayama, a woman found a 10-foot long earthworm while tilling the soil. Another farmer in the same prefecture found a still thrashing piece of a worm that had been cut off during farm work. The piece is estimated to have come from a worm 11.5 to 13 feet long. Another farmer in the same area found a piece of an earthworm, that was accidentally cut during farm work, that he estimated was 11 to 13 feet long. Other reports of giant worms, albeit smaller, have been reported on Shikoku Island, Shizuoka and Nara.