Sao Tome giant treefrog (Hyperolius thomensis)

Synonyms: Nesionixalus thomensis
GenusHyperolius (1)
SizeMale length: 27 - 41 mm (2)
Female length: 36 - 49 mm (2)

The São Tomé giant treefrog is classified as Endangered (EN) on the IUCN Red List (1).

As the largest member of the genus Hyperolius, the large, flamboyant São Tomé giant treefrog (Hyperolius thomensis) presents a classic example of ‘island gigantism’, the tendency of certain colonisers on islands to evolve to become larger than their mainland relatives (2) (3) (4).

While the back of the São Tomé giant treefrog is a uniform green to blue-green colour, the underside is attractively marbled with orange, white and black. In the male São Tomé giant treefrog, the back is densely studded with small spines (2).

Like other species within the genus, the São Tomé giant treefrog has expanded toe pads and long legs that make it an adept climber (5) (6).

The São Tomé giant treefrog is endemic to the island of São Tomé in the Gulf of Guinea, 255 kilometres off the coast of Gabon (1) (2) (7).

The São Tomé giant treefrog is restricted to the remnants of original primary forest that occur at elevations above 800 metres (1) (2).

Like many other Hyperolius species (8), the São Tomé giant treefrog breeds in standing water, but instead of utilising slow streams or ponds, this remarkable species lays its eggs in water-filled holes in trees, often at a considerable height (1) (2) (3).

The eggs are deposited in masses of 20 to 40 (2), and the same tree hole may be used for breeding by several different individuals at different times (1). Like most other frogs, the eggs develop into free-swimming, gilled tadpoles, which then metamorphose into the adult form (3). 

Forest clearance began on São Tomé in the late 15th century, when early colonisers made space for the cultivation of sugar cane. In the 1800s the rate of deforestation accelerated dramatically, first with the production of coffee and later with cocoa. At one stage in the early 20th century, São Tomé was the world’s largest producer of cocoa, with an estimated 42 percent of the island being devoted to its production. The crash in the price of cocoa, and the island’s conversion to independence in 1975, significantly slowed down the rate of forest clearance, but not before almost all the island’s lowland primary forest had been destroyed (9).

Since the São Tomé giant treefrog is so notoriously difficult to find, very little is known about its population status or the threats it faces, but habitat loss is likely to continue to have the biggest impact on this species (1). This species also seems to be occasionally offered in the pet trade in Europe, although the extent to which this occurs and impacts the population is unknown (3).

There are no known specific conservation measures in place for the São Tomé giant treefrog, but this species does occur in the protected Obo National Park (1). 

Find out more about the fauna and flora of São Tomé:

Find out more about amphibian conservation:

Authenticated (08/11/11) by Olivier S. G. Pauwels, Research Associate at the Royal Belgian Institute for Natural Sciences, Brussels, Belgium.

  1. IUCN Red List (March, 2010)
  2. AmphibiaWeb (March, 2010)
  3. Island Biodiversity Race (March, 2010)
  4. Shugart, H.H. (2004) How the Earthquake Bird Got its Name and Other Tales of an Unbalanced Nature. Yale University Press, New Haven.
  5. Halliday, T. and Adler, K. (2002) The New Encyclopedia of Reptiles and Amphibians. Oxford University Press, Oxford.
  6. Duellman, W.E. and Trueb, L. (1994) Biology of Amphibians. Johns Hopkins University Press, Baltimore.
  7. Drewes, R. C. and Wilkinson, J.A. (2004) The California Academy of Sciences Gulf of Guinea Expedition (2001). The taxonomic status of the genus Nesionixalus Perret, 1976 (Anura: Hyperoliidae), treefrogs of São Tomé and Príncipe, with comments on the genus Hyperolius. Proceedings of the California Academy of Sciences, 55: 395-407.
  8. Wells, K. D. (2007) The Ecology and Behavior of Amphibians. University Of Chicago Press, Chicago.
  9. Peet, N. and Atkinson, P. (1994) Biodiversity and conservation of the birds in São Tomé and Príncipe. Biodiversity and Conservation, 3(9): 851-868.