Reptiles and Amphibians of Thailand

Thailand's Snakes, Lizards, Turtles, and Frogs

Spotted Slug Snake

Pareas macularius

This species is found in Thailand, but not within Bangkok itself
Spotted slug snake Pareas macularius งูกินทากจุดดำ ngu gin thaag jud dam Phu Hin Rong Kla national park thailand
Spotted Slug Snake in Phu Hin Rong Kla NP (Thai National Parks / CC BY-SA)

English name: Spotted Slug Snake (aka “Spotted Slug-eating Snake”, “Mountain Slug Snake”)
Scientific name: Pareas macularius
Thai name: งูกินทากจุดดำ (Ngu Gin Thaag Jud Damm)

Description: To 60 cm. Slightly vertically compressed body is brownish-gray to gray with prominent black-and-white spots that form something like broken crossbars. There is a whitish W-shaped collar on the neck that is filled with light brown speckles, though sometimes the speckling obscures the collar completely. The upper rows of dorsal scales are weakly keeled.

Similar Species: White-spotted Slug Snake is smaller, has smooth scales on top of the body, and often has a colored collar that is not shaped as a W.

Range: Due to earlier confusion regarding its description it is unclear where true Spotted Slug Snakes are found. They appear to be present throughout Thailand except in the extreme south and are likely in neighboring countries as well including Myanmar, China, Laos, Vietnam, and Cambodia.

Habitat: Mature evergreen forest. Sjon Hauser has found that this species appears limited to elevations above 800m in northern Thailand, though in other habitat types in southern Thailand it can be found as low as 300-400m elevation.

Place in the ecosystem: Like most other slug snakes it feeds primarily on snails as well as slugs. It may be eaten by larger snakes, nocturnal birds and carnivorous mammals such as civets.

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

Conservation status and threats: As mentioned before the confusion regarding its identity makes current status uncertain. It appears to be fairly common and likely has a wide range, though as with all slug snakes it is threatened by deforestation.

Interesting facts: In 2004 a researcher decided that Spotted Slug Snakes were the same species as White-spotted Slug Snakes and thus declared the Spotted Slug Snake to be invalid. He based this determination on an inability to distinguish between records of the two species in China. Several other researchers felt that this lumping was invalid. Since 2004 both genetic and morphological studies show the species to be separate, although they indeed may have been confused often in the past. In a 2017 paper Sjon Hauser demonstrated that Spotted Slug Snakes differ from White-spotted Slug Snakes in that they have weakly keeled scales, are larger on average, have a different type of collar, more speckling on the lips and venter, and are found at higher elevations.

Slug snakes have a specialized hook-like jaw with more teeth on the right-hand side than on the left. This rare “non-symmetric” 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 the 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.

References:
On the validity of Pareas macularius
Sjon Hauser pers. comm.
Asymmetrical Snakes
Serpents of Thailand

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