Fowlea piscator
This species is found in Thailand, but not within Bangkok itself
India (Jon Hakim / CC BY-NC) 
India (Jon Hakim / CC BY-NC-SA) 
India (Jon Hakim / CC BY-NC-SA) 
India (Jon Hakim / CC BY-NC-SA)
English name: Checkered Keelback
Scientific name: Fowlea piscator (formerly Xenochrophis piscator)
Thai name: งูลายสอใหญ่ (Ngu Lai-so Yai)
Description: Up to 1m long. Body of average girth. Eyes are large. Body is olive-brown to tan, yellow-brown, or gray with a black checkered pattern (faded in some populations). In parts of South Asia the black marks expand into large blotches. Two black streaks come down and back from the eye, and in some specimens there is an inverted black “V”-mark on the neck with the point facing the head. Juveniles have a characteristic yellow mark on their neck that fades with age.
Similar Species: Yellow-spotted Keelback has a black streaks and blotches on the side rather than a checker pattern and has a “Y” mark on the neck with the opening facing the head.
Red-necked Keelback is more colorful and has a characteristic red neck. Juvenile Red-necked Keelbacks, which may not have developed the red neck yet, have a large black marking on the back of their neck that juvenile Checkered Keelbacks do not have.
Range: Pakistan and India across south Asia east to Laos and north/central Thailand.
Habitat: In or near marshes, ponds, or rice patties, sometimes in the middle of urban areas.
Contribution to the ecosystem: The Checkered Keelback eats fish, frogs, rodents, birds, and smaller snakes. The juveniles are eaten by larger snakes and birds.
Danger to humans: Will bite aggressively when provoked and can draw blood, but is not dangerous to humans. Though it has no venom glands, some people report itching and slight swelling after a bite.
Conservation status and threats: No known conservation threats.
Interesting facts: The Checkered Keelback and Yellow-spotted Keelback were once considered different color variations of the same species. They have since been split into different species, with the Checkered Keelback being found to occur only in western Thailand, Burma, southern China, Bangladesh, and India, but not in Bangkok.
The Checkered Keelback is one of the most adaptable snakes I have ever seen, able to survive in crowded cities and under water conditions that kill off most other native wildlife. It can be found almost any place where there is water and vegetation to hide in, and in much of its range it is the most commonly found snake.
References:
Snakes of Taiwan: Xenochrophis piscator
On the taxonomy of the Xenochrophis piscator complex
A Photographic Guide to Snakes and Other Reptiles of Peninsular Malaysia, Singapore and Thailand
A Field Guide to the Reptiles of South-East Asia
Reptiles and Amphibians of Thailand 