Purple frog  (Nasikabatrachus sahyadrensis)

The purple frog is classified as Endangered (EN) on the IUCN Red List (1).

The sole surviving member of an ancient group of amphibians that evolved some 130 million years ago, the discovery of the purple frog (Nasikabatrachus sahyadrensis) has been described as a ‘once-in-a-century find’ (3) (4). This frog has a highly distinctive and somewhat comical appearance, with a hugely bloated body and short, stout limbs (2) (5). The small head seems almost too short for the body and the peculiar narrow snout ends in a white, knob-like protrusion (2) (3). The small, yet conspicuous eyes sit above a narrow mouth, which has a flexible lower jaw that allows the short and rounded tongue to protrude while feeding (2).

Adapted to a burrow-dwelling lifestyle, the purple frog has a shovel-shaped tubercle on each hindlimb and rounded toe-tips on the webbed feet that enable it to dig into the moist ground (2) (5). The smooth skin is dark purple on the upperside, fading to grey on the underside (5).

The purple frog is endemic to the Western Ghats of India, where it is known from only Kattapana and near Idukki town in the Cardamom Hills of Kerala State (1) (5).

The purple frog is known from disturbed secondary forest near evergreen montane forest and cardamom plantations, although it probably also inhabits undisturbed forest. This burrow-dwelling frog requires fairly loose, damp and well-aerated soil in close proximity to permanent or temporary ponds and ditches or streams (1) (5).   

For most of the year this burrow-dwelling frog lives 1.3 to 3.7 metres under the ground in a cavity that it excavates by digging downwards, using its hindlimbs like spades to throw the soil over its back (1) (5) (6). While foraging, the purple frog actively seeks out termite prey with its touch-sensitive snout, using the robust conical-shaped head to penetrate termite tunnels before sucking up its prey with its fluted tongue. While resting, the limbs are tucked under the body in a horizontal position (5) (6).

For several weeks of the year the purple frog comes to the surface to breed (1) (2) (5). Frogs gather around pools and the sides of streams, and once partners have paired up, the male grasps the female just above the legs and, using sticky skin secretions, glues to her in amplexus (the mating embrace) (2) (5). The fertilised eggs are laid in a pool of water and will subsequently hatch into tadpoles, before going through varying stages of metamorphosis to become adult frogs (5).

Known from only 135 individuals, of which only three are female, the purple frog is thought to be an extremely rare species. The main threat to this elusive frog is the loss of its forest habitat to encroaching agriculture (1). Within the Western Ghats, over 90 percent of the forest has been lost, with conversion to coffee, cardamom, ginger and other crop plantations the most significant agents (1) (2). The potential for dam developments to inundate vast areas of its habitat also mean that the status of the purple frog is extremely precarious (7).

Due to its threatened status and evolutionary distinctiveness, the purple frog is categorised as a focal species on the Zoological Society of London’s EDGE of Existence programme. This project aims to highlight the need for the conservation of this unique species, while establishing a set of conservation priorities and, as a result, studies are currently being undertaken to investigate the purple frog’s ecology and threats (5). 

As the purple frog is not known from any protected areas, reserves must be established or extended to protect its remaining habitat (1). It would also benefit from the development of a species action plan and the involvement of the local community in conservation work. However, depending upon the success of these measures, it is hoped that this Endangered frog could become a flagship species for conservation in the area (5) (7).

View information on this species at the UNEP World Conservation Monitoring Centre.

For more information on the conservation of the purple frog, see:

• EDGE of Existence:
  http://www.edgeofexistence.org/amphibians/species_info.php?id=549