Chōmei

The is a demon kabutomushi sealed within Fū from Takigakure. It resembles a gigantic, blue rhinoceros beetle, with six of its seven tails resembling green insect wings, along with the seventh tail, all growing from the end of its abdomen. It has been captured, extracted, and sealed by Akatsuki.

Background
According to Madara Uchiha, the Seven-Tails came into being in the waning days of the Sage of the Six Paths' life; to prevent its resurgence, the Sage split up the chakra of the Ten-Tailed Beast into nine separate, monstrous constructs of living chakra, which would become known as the tailed beasts.