Halicephalobus mephisto: Deep‑Earth ‘Devil Worm’ Shows Subsurface Life

Scientists have studied the microscopic nematode Halicephalobus mephisto, nicknamed the “devil worm,” which inhabits the deep terrestrial subsurface at about 1.3 km below the surface. The worm survives in hot, dark, high‑pressure conditions by feeding on abundant bacteria that form orange‑white mats, and its tiny body—only a few human hairs thick—acts as a “whale” in this miniature ecosystem.

The species was first discovered in 2011, overturning the previous belief that life could not exist more than 30 cm beneath the ground. Researchers such as geomicrobiologist Karen Lloyd of the University of Southern California and Belgian biologist Gaetan Borgonie of the Extreme Life Isyensya institute have cultivated descendants of the worm to investigate how it endures the extreme environment and to explore what other unseen life forms may exist deep within the Earth.