Reptiles and Amphibians of Thailand

Thailand's Snakes, Lizards, Turtles, and Frogs

Keeled Slug Snake

Pareas carinatus

This species is found in Thailand, but not within Bangkok itself
Keeled Slug Snake Pareas carinatus yala thailand งูกินทากเกล็ดสัน (Ngu Gin Thaag Gled Sann)
Keeled Slug Snake in Yala Province (Leonid / CC BY-NC)

English name: Keeled Slug Snake (aka “Keeled Slug-eating Snake”)
Scientific name: Pareas carinatus
Thai name: งูกินทากเกล็ดสัน (Ngu Gin Thaag Gled Sann)

Description: To 75 cm. Its slender, vertically compressed body is tan, brown or grayish-brown with faint dark crossbars. The blunt, distinct head is the same color as the body with a black eyestripe going back of the eye.

Relevant scale counts: Prefrontal scale is separated from the eye by a couple small preorbital scales. As the name implies, the dorsal scales are keeled.

Similar Species: Hampton’s Slug Snake has prefrontal scale in contact with the eye and is typically more slender and with a brighter orange tint in life.
Smooth Slug Snake has no keeled dorsal scales, is often darker in color, and sometimes has a light dorsal stripe.
Malayan Slug Snake has a striking white head followed by an extensive black blotch on the neck.
Blunt-headed Slug Snake has a shorter and deeper head along with a more slender body and a unique broad vertical eyestripe.
Juvenile Black-headed Cat Snakes have a broader head, a longer snout, and smooth scales.

Range: Throughout Thailand as well as west to Myanmar, north to southern China, east to Laos, Vietnam, and Cambodia, and south through Malaysia and much of Indonesia.

Habitat: Moist areas in lowland forests up to 1000 meters in elevation.

Place in the ecosystem: The Keeled Slug Snake appears to primarily or exclusively feed on snails – in one experiment it refused slugs altogether. It may be eaten by larger snakes, nocturnal birds and carnivorous mammals such as civets.

Danger to humans: The Keeled Slug Snake is no danger to humans.

Conservation status and threats: This species is thought to be decreasing due to continuing deforestation in southeast Asia. However, it is still widespread and common so it is not in immediate danger.

Interesting facts: Most slug snakes have a specialized hook-like jaw with more teeth on the right-hand side than on the left. This rare “asymmetric” feature came about because the snails they prey on tend to have right-handed twisting shells, therefore making it easier for the snake to get the right side of its mouth into the shell than the left side. In fact, studies have shown that some slug snakes are far more successful at extracting snails out of those right-handed shells than they are when faced with a snail in a left-handed twisting shell.

The Keeled Slug Snake is slightly different in that it appears to be able to prey on “right-handed” and “left-handed” snails with equal efficiency. Its jaw and teeth are less asymmetric than most other slug snake species and it often strikes differently towards the unusual “left-handed” snails, extracting them in the opposite orientation. This may be a case where slug snakes evolved to prey on right-handed snails, and when left-handed snails in the region increased as a result, at least one species has started evolving back!

References:
Ecology Asia: Keeled Slug Snake
IUCN Red List: Keeled Slug-eating Snake
Sjon Hauser pers. comm.
Asymmetrical Snakes
Subtle asymmetries in the snail-eating snake Pareas carinatus
Predatory Behavior of the Snail-Eating Snake Pareas carinatus
A snail-eating snake recognizes prey handedness
Serpents of Thailand

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