Devil’s worm (Halicephalobus mephisto)

GenusHalicephalobus (1)
SizeLength: c. 0.5 mm (1) (2)
Top facts

The Devil’s worm has not yet been classified on the IUCN Red List.

Thought to be the world’s deepest-living animal (2) (3), the Devil’s worm earned its interesting name for the fact that it is found at a depth of more than one kilometre into the Earth’s crust (1) (2) (4). The scientific name of this newly discovered nematode, mephisto, is derived from Mephistopheles, the demon of medieval mythology featured in the Faustian legend (1) (2) (3).

The Devil’s worm is only about 0.5 millimetres long (1) (2), and can be distinguished from other species within the Halicephalobus genus by the presence of a relatively long tail (1). This tail is between 110 and 130 micrometres in length, and has a thread-like tip. The body of the Devil’s worm is usually straight, and is made up of rings (1).

At present, the Devil’s worm is only known from the Beatrix Gold Mine in South Africa (1) (3) (4), located approximately 240 kilometres southwest of Johannesburg (4).

The Devil’s worm was discovered in fracture water encountered in Beatrix Gold Mine in South Africa (1), at a depth of more than a kilometre into the Earth’s crust (1) (2) (4). This water is believed to be hypoxic, meaning that it has a low level of dissolved oxygen (1), and carbon dating procedures have estimated that the fracture water has not been in contact with the Earth’s atmosphere for upwards of 4,000 years (1) (2) (3).

The Devil’s worm is known to tolerate immense underground pressure (2), as well as high temperatures (1), and was found in an environment which reached around 37 degrees Celsius (2) (4).

Little information is available on the biology of the newly discovered Devil’s worm. However, this species demonstrates a high temperature tolerance (1) (2), higher than most terrestrial nematodes (4), and is thought to be able to survive in conditions of up to 41 degrees Celsius (1). Nematodes are known to be able to enter a state of suspended animation known as anabiosis (1), although as yet there are no records of this for the Devil’s worm.

The Devil’s worm feeds on accumulations of bacteria, known as ‘biofilms’, which are found on the water’s surface (1) (3) (4). This species reproduces asexually through parthenogenesis (1).

The unearthing of the Devil’s worm is a significant one, as prior to its discovery nematodes were not known to occur beyond depths of tens of metres (3). This new discovery is also viewed as having important implications for the potential of encountering subterranean life forms on other planets (2).

There is currently no information available on the potential threats to the Devil’s worm.

There are currently no known conservation measures in place specifically for the Devil’s worm.

Find out more about the Devil’s worm and its discovery:

Learn more about newly discovered species:

This information is awaiting authentication by a species expert, and will be updated as soon as possible. If you are able to help please contact:

  1. Borgonie, G., García-Moyano, A., Litthauer, D., Bert, W., Bester, A., van Heerden, E., Möller, C., Erasmus, M. and Onstott, T.C. (2011) Worms from hell: Nematoda from the terrestrial deep subsurface of South Africa. Nature, 474: 79-82.
  2. International Institute for Species Exploration - Arizona State University: Top 10 - 2012. What the Devil?! (January, 2013)
  3. Mosher, D. (2011) New "Devil worm" is deepest-living animal. National Geographic News, 1 June. Available at:
  4. Drake, N. (2011) Subterranean worms from hell. Nature News, 1 June. Available at: