This species is found in Thailand, but not within Bangkok itself
English name: Southeast Asian Bockadam (aka “Dog-faced Water Snake”)
Scientific name: Cerberus rynchops
Thai name: งูปากกว้างน้ำเค็ม (Ngu Pak Kwang Nam Khem)
Description: To 120cm long. Relatively slender, cylindrical body for a water snake. Head is wider than neck with thick fleshy cheeks. A dark eyestripe passes through the relatively small eyes. Body is brownish or grayish with dark crossbars, with a venter that is mottled gray and cream.
Relevant scale counts: Usually 25 midbody scale rows (sometimes 23) of keeled scales. The last two upper labials are both horizontally divided with keeled scales directly behind them at the jaw angle.
Similar Species: Southeast Asian Bockadam (Dog-faced Water Snake) usually has 23 midbody scale rows, only the last upper labial is horizontally divided, and there are no keeled scales in front of the jaw angle
Martaban Water Snake is brown with light saddles edged in black and lacks the horizontally protruding eyes.
Keel-bellied Water Snake has a lighter cream-to-yellow body with no clear dorsal/ventral contrast.
Bocourt’s Water Snake has a thicker, darker body and typically only found in freshwater settings.
Range: The South Asian Bockadam is found along coastal areas from Mumbai in India east across Sri Lanka, Bangladesh, and Burma. The exact transition point between this species and the Southeast Asian Bockadam (Dog-faced Water Snake) is unknown but is certainly north of Phuket, Thailand. Whether or not the South Asian Bockadam reaches a portion of the western Thai coastline is yet to be determined.
Habitat: This species is found in mangrove mudflats and brackish river mouths, only occasionally venturing upriver.
Place in the ecosystem: Eats fish and sometimes crustaceans. May be eaten by larger snakes, large fish, monitors, and wading birds.
Danger to humans: The South Asian Bockadam is rear-fanged but its venom is not considered a threat to humans.
Conservation status and threats: In some areas these snakes are collected for their skins, but the species still appears to be quite common where found.
Interesting facts: It was once believed that the Dog-faced Water Snake was a single species that ranged across Asia from India to the Philippines, but a 2012 paper by Murphy, Voris, and Karns split the species, with the South Asian Bockadam (C. rhynchops) occurring from India to Burma while the Southeast Asian Bockadam (C. scheneiderii) occurs from Thailand and Malaysia through Indonesia and the Philippines. Three more range-limited species occur in Australia, Micronesia, and a freshwater lake in the Philippines.
The South Asian Bockadam can be incredibly prevalent in the mangrove mudflats. During the daytime none of the snakes will be visible as they hide in crab holes or under water, but in the night at low tide they will cover the landscape. I have had the good fortune of going on boat trips along mudflats at night where 40+ South Asian Bockadam could be seen within a single hour-long pass.
The Dog-faced Water Snakes, a revision of the genus Cerberus
IUCN Redlist: Cerberus rynchops
A Checklist and key to the Homolopsid snakes
Evolution in the Mud
A Photographic Guide to Snakes and Other Reptiles of Peninsular Malaysia, Singapore and Thailand