Family : HOMALOPSIDAE
Species : Cerberus schneiderii
Maximum Size : up to 108 cm

The Dog-faced Water Snake (Cerberus schneiderii), or Schneider's Bockadam, is a common, and often locally abundant inhabitant of Southeast Asia's mangroves and mudflats. This species emerges in great numbers at night during low tide to feed on fish and invertebrates.

The dorsal colour is greyish brown, and the ventral surface brown with white patches or cream-coloured and mottled. There is a black line from the eye to the neck, and its eyes are located on top of the head, allowing it to maintain vision when half-submerged in the mud. Though a mildly venomous, back-fanged species it is generally not aggressive. 

The species has other physical and behavioural adaptations to its ecological niche, such as nostrils which can be closed by a valve-like structure to exclude water, salt-secreting glands, and the ability to efficiently 'sidewind' across slippery mudflats.

Schneider's Bockadam occurs in coastal areas of Vietnam, Cambodia, Thailand, Peninsular Malaysia, Singapore, the Philippines and the whole of Indonesia (excluding New Guinea).

Based on Murphy et al (2012), who revised the genus Cerberus, in addition to C. schneiderii there are four other species in the genus, three of which occur in Southeast Asia as follows :

- C. rynchops, the Karoo Bockadam, which occurs along the coastline of Burma (Myanmar), as well as Bangladesh, India and Sri Lanka.

- C. australis, the Australian Bockadam, which occurs in parts of eastern Indonesia, as well as the southern coastline of New Guinea, and the northern coastline of Australia.

- C. microlepis, the Lake Buhi Bockadam, which is a land-locked, freshwater species confined to the Philippine island of Luzon.

The remaining species, C. dunsoni, the Palau Bockadam, is endemic to the pacific island of Palau.

The term 'Dog-faced Water Snake' may apply to any of the five species of Cerberus.

 
Fig 1 : Full-grown specimen of Schneider's Bockadam in the mangroves of Khatib Bongsu, Singapore.

Fig 2 : Specimen emerging from a burrow on the mudflats of Sungei Buloh, Singapore.

Fig 3 : Example from Muar, Peninsular Malaysia, on the intertidal mudflats which face the Straits Of Malacca.

Fig 4 : Typical posture when hunting for small fish.

Fig 5 : A successful catch being consumed by the banks of a mangrove inlet, Singapore.

Fig 6 : A 75 cm specimen tries unsuccessfully to catch small fish in the Malacca River, Peninsular Malaysia.

Fig 7 : The pale, worn out skin and opaque eye scale of this specimen indicate it is ready to shed its old skin.  Seen at Pasir Ris, Singapore.


References : H2, H3
Murphy, John C; Voris, Harold K. & Karns, Daryl R. 2012. The Dog-faced Water Snakes, A Revision of the Genus Cerberus Cuvier, (Squamata, Serpentes, Homalopsidae), with the Description of a New Species. Zootaxa 3484:1-34.