Naja siamensis is classified under the
genus Naja of the
family Elapidae. It was first described by
Austrian-born Italian zoologist Josephus Nicolaus Laurenti in 1768. The
generic name
Naja is a Latinisation of the
Sanskrit word
nāgá (
नाग), meaning "cobra". The
specific epithet
siamensis is derived from the word
Siam or
Siamese, which means "relating to or characteristic of Thailand or its people and language".
[9] This species was long confused with the
monocled cobra (
Naja kaouthia) and the
Chinese cobra (
Naja atra), and extensive variation in pattern and scalation contributed to this confusion. Detailed morphological and molecular analyses revealed it to be a distinct species during the 1990s.
[3][10]
Distribution and habitat[edit]
It is found in Southeast Asia, including
Thailand,
Cambodia,
Vietnam, and
Laos. May occur in eastern
Myanmar but no records are known.
[3] It has been reported from Taiwan where it was released to the wild based on folklore Buddhist practices.
[11] It occupies a range of habitats including lowlands, hills, plains, and woodland.
[5] It can also be found in jungle habitat and it is sometimes attracted to human settlements because of the abundant populations of rodents in and around these areas.
[12]
Behavior and diet[edit]
It is a primarily
nocturnal species.
[12] It shows variable temperament depending on the time of day it is encountered. When threatened during daylight hours, the snake is generally timid and seeks refuge in the nearest burrow.
However, when the snake is threatened at night, it is more aggressive and is more likely to stand its ground, rear up and display its hood and spit out its venom.[13] If spitting venom doesn't work, it will strike and bite as a last resort. When biting, this species tends to hold on and chew savagely. It usually feeds on rodents, toads, and other snakes.[4][12]
Reproduction[edit]
The snake is
oviparous. The female will lay 13-19 eggs
[4] 100 days after
oviposition. Eggs will hatch after 48 to 70 days depending on the temperature of incubation. Offspring are independent as soon as they have hatched. Hatchlings are anywhere from 12 to 20 cm long and, because they possess fully developed venom delivery systems, should be treated with the same respect as adults.
[13] Some hatchlings can be as long as 32 cm.
[5]
Like most other
spitting cobras, its venom is primarily a postsynaptic
neurotoxin and
cytotoxin (necrotizing or tissue-death).
[4] Like all cobras, this species shows variation in venom toxicity based on different factors (diet, locality, etc.). In a study of specimens from Thailand, the
IV LD50 was 0.28 μg/g (0.18-0.42 μg/g).
[14] Fischer and Kabara (1967) listed a value of 0.35 mg/kg via
IP route.
[15] Another study gave an
LD50 range. Deaths, which generally happen due to paralysis and consequent asphyxiation, mainly occur in rural areas where the procurement of
antivenin is difficult. 1.07-1.42 mg/gram of
mouse body weight.
[16] Bite symptoms include pain, swelling and
necrosis around the wound.
The bite of this snake is potentially lethal to an adult human.
If the snake spits venom into the eyes of an individual, the individual will experience immediate and severe pain as well as temporary and sometimes even permanent blindness.
[3][13]
In a national hospital based survey of snakes responsible for bites in Thailand,
10% of all dead snakes brought by snake-bitten patients were of this species (described as "Naja atra northern spitting cobra"). Neurotoxic signs (ptosis and difficulty in breathing) were observed in 12 of the 114 cases (10.5%). Local swelling and necrosis were common, but many of the patients were followed up for too short a time to allow precise assessment of the incidence of these effects. Swelling and necrosis, comparable in all respects with that following bites by
N. kaouthia, in patients envenomed by
N. siamensis in Ubon and Kanchanaburi in Thailand.
