This is a Shovel-headed Garden Worm, (Bipalium kewense), and no one knows where its native habitat is. It was discovered in the soil of imported plants in the greenhouses at Kew Gardens, England in 1878. It has been found in potting soil and imported plants in many parts of the world, and had been spread by people before being discovered. It is thought to have originated in Southeast Asia, but that has not been confirmed.