Laticauda colubrina, commonly known as the banded sea krait, colubrine sea krait, or yellow-lipped sea krait, is a species of venomous sea snake found in tropical Indo-Pacific oceanic waters. The snake has distinctive black stripes and a yellow snout, with a paddle-like tail for use in swimming.
The banded sea krait spends much of its time underwater in order to hunt, but returns to land to digest, rest, and reproduce. It has very potent neurotoxic venom, which it uses to prey on eels and small fish. Because of their affinity to land, banded sea kraits often encounters humans, but the snakes are not aggressive and only attack in self-defense.
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- See snake scales for terms used
Ventrals are large (wide), one-third to more than half the width of the body; nostrils are lateral; nasals are separated by internasals; 21–25 longitudinal rows of imbricate dorsal scales are found at midbody; an azygous prefrontal shield is usually present; and the rostral is undivided.
The body is subcylindrical, only slightly laterally compressed. The rostral is higher than broad; an azygous shield separates the prefrontals, but sometimes is absent; the frontal is considerably longer than its distance from the end of the snout; one preocular and two postoculars are present; there are 7–8 supralabials, the 3rd–4th touching the eye; temporals are 1+2; five infralabials are in contact with the genials, both pairs of which are usually well developed and in contact with one another, the anterior pair smaller than the posterior; a double series of elongated scales, the inner series the larger, occur at the oral margin. Dorsal scales are in 21–23 rows (rarely 25). Ventrals number 213 to 245, and are about four times as wide as long. Subcaudals in males number 37–47, and in females 29–35.
Total length: males 875 mm (34.4 in), females 1,420 mm (56 in); tail length: males 130 mm (5.1 in), females 145 mm (5.7 in).
In colour these snakes are light or dark bluish grey above, yellowish below, with black rings more or less of uniform width throughout or narrowing on the belly (some of them interrupted below). The upper lip is yellow, and the snout is yellow, the colour extending backward on each side of the head above the eye as far as the temporal shields, leaving a dark bar in between.The rest of the head is black.
Female snakes are longer than male snakes and move faster.
Range and habitat
The banded sea krait is widespread throughout the eastern Indian Ocean and Western Pacific. It can be found from the eastern coast of India, along the coast of the Bay of Bengal in Bangladesh, Myanmar and other parts of Southeast Asia, to the Malay Archipelago and to some parts of southern China, Taiwan, and the Ryukyu Islands of Japan. The species is also common on Fiji and other Pacific islands within its range. Vagrant individuals have been recorded in Australia, New Caledonia, and New Zealand.
The venom of the banded sea krait is a very powerful neurotoxic protein, with a LD50 in rodents of about 0.44 mg per kilogram of body weight. The venom is an α-neurotoxin that disrupts synapses by competing with acetylcholine for receptors on the postsynaptic membrane, similar to erabutoxins and α-bungarotoxins.
Some varieties of eels, which are a primary food source for sea kraits, may have coevolved resistance to banded sea krait venom. Gymnothorax moray eels taken from the Caribbean, where the banded sea krait is not present, died after injection with doses as small as 0.1 mg/kg body weight, but Gymnothorax individuals taken from New Guinea, where banded sea kraits are endemic, were able to tolerate doses as large as 75 mg/kg without severe injury.
Banded sea kraits are present on land and in water and represent an intermediate stage between aquatic and terrestrial life. Juveniles stay in water and on adjacent coast, but adults are able to move further inland and spend half their time on land and half in the ocean. Adult males are more terrestrially active during mating and hunt in shallower water, requiring more terrestrial locomotive ability. On the other hand, adult females are less active on land during mating and hunt in deeper water, requiring more aquatic locomotive ability.
When hunting, sea kraits frequently head into deep water far away from land, but return to land in order to digest, shed skin, and reproduce. Individual kraits return to their specific home islands, exhibiting philopatry. One study found that when sea kraits on Fijian islands were relocated to different islands 5.3 km away, all recaptured individuals were found on their home islands in an average of 30.7 days.
Body adaptations, especially a paddle-like tail, help banded sea kraits swim. These adaptations are also found in other Hydrophiinae sea snakes because of convergent evolution. However, because of the differences in motion between crawling and swimming, these same adaptations impede the snake's terrestrial motion. On dry land, banded sea kraits can still move, albeit slower than swimming. In contrast, most other non-Laticauda sea snakes are virtually stranded on dry land.
Hunting and diet
Banded sea kraits often hunt alone, but have also been recorded in large numbers in the company of hunting parties of giant trevally and goatfish. This cooperative hunting technique is similar to that of the moray eel, with the kraits flushing out prey from narrow crevices and holes, and the trevally and goatfish feeding on fleeing prey.
While probing crevices with their head, sea kraits are unable to observe approaching predators and could be vulnerable. The snakes can deter predators by fooling them that their tail is the head, because the color and movement of the tail is similar to that of the snake's head. For example, the lateral aspect of tail corresponds to the dorsal view of the head.
Kraits primarily feed on varieties of eels, but also eat small fish. Male and female kraits exhibit sexual dimorphism in hunting behavior, as adult females, which are significantly larger than males, prefer to hunt in deeper water for larger conger eels, while adult males hunt in shallower water for smaller moray eels. In addition, females hunt for only one prey item per foraging bout, while males often hunt for multiple items. After hunting, the kraits return to land in order to digest their prey.
Courtship and reproduction
Every year during the warmer months of September through December, male banded sea kraits gather on land and in the water around gently sloping areas at high tide. Male kraits prefer to mate with larger female kraits because they produce larger and more offspring.
When a male detects a female snake, it chases the female and begins courtship. Female kraits are much larger and many males will escort and intertwine around a single female. The males then align their bodies with the female and rhythmically contract; the resulting mass of snakes can remain nearly motionless for several days. After courtship, the snakes copulate for about an average of two hours.
The female kraits then lay as many as 10 eggs per clutch. The eggs are deposited in crevices where they remain until hatching. These eggs are very rarely found in the wild; only two nests have been definitively reported throughout the entire range of the species.
Interaction with humans
Because banded sea kraits spend much of their time on land, they are often encountered by humans. They are frequently found in the water intake and exhaust pipes of boats. Kraits are also attracted to light and can be negatively distracted by artificial sources of light, including hotels and other buildings, on coasts.
There are fewer recorded bites from this species compared to other venomous species such as cobras and vipers as it is less aggressive and tends to avoid humans. If they do bite, it is usually in self-defense when accidentally grabbed. Most sea snake bites occur when fishermen attempt to untangle the snakes from their fishing nets.
In the Philippines, banded sea kraits are caught for their skin and meat; the meat is smoked and exported for use in Japanese cuisine. The smoked meat of the black-banded sea krait, a related Laticauda species, is used in Okinawan cuisine to make irabu-jiru (Japanese: イラブー汁, irabu soup).
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