Sea snakes may regularly appear in lists of the world’s most venomous creatures, but in reality these marine reptiles – of which there are more than 60 species – represent little danger to humans.
Falling into two groups that evolved independently of each other – true sea snakes and sea kraits – these amazing creatures showcase a range of fascinating adaptations to life in the water.
What do sea snakes look like?
Markings vary from species to species but many sea snakes have alternating bands of black, grey, blue or white. Sea snakes have a pair of short fangs at the front of the mouth, which remain hidden in a fold in the gums until they emerge for biting prey.
How big are sea snakes?
Size depends on species too, with some as small as 50cm long and others growing to 2.7m, but most are about 1.m long. They weigh between 0.6-1.8kg.
Are sea snakes dangerous?
Sea snakes have some of the deadliest venom around (with the Dubois’ sea snake above thought to top the list), containing powerful toxins that can cause paralysis, including of the diaphragm, potentially leading to respiratory failure.
Fortunately, it’s rare to hear of sea snakes causing harm to humans – sea snakes are not aggressive, have short fangs and release only a small quantity of venom with each bite.
Those most at risk from sea snake bites are fishers attempting to remove sea snakes accidentally entangled in their nets – the beaked sea snake (one of the deadliest sea animals), which is regularly encountered by fishers off India, is thought to be responsible for the most human fatalities.
How have sea snakes adapted to life in the water?
True sea snakes – those that spend the majority of their lives in the water – have a flattened body and oar-like tail that enable them to swim with an undulating motion. Smaller scales on the belly also ease their passage through the water.
Sea kraits – of which there are less than 10 known species, compared to the more than 50 true sea snakes – are less well adapted, thanks to the fact that they spend up to half their lives on land. They have retained their enlarged belly scales and cylindrical body, enabling them to crawl on land (unlike true snakes, which can barely move outside the water).
How do sea snakes breathe?
A true sea snake’s nostrils are positioned on top of its snout (rather than to the sides, as in terrestrial species) to aid breathing at the surface.
An enlarged lung that extends the entire length of the sea snake’s body enables larger air intake, and helps with buoyancy at the surface too. Glands under the sea snake’s tongue are used to excrete excess salt.
Sea kraits – of which there are less than 10 known species, compared to the more than 50 true sea snakes – are less well adapted, thanks to the fact that they spend up to half their lives on land. They have retained their enlarged belly scales and cylindrical body, enabling them to crawl on land (unlike true snakes, which can barely move outside the water).
How long can sea snakes stay submerged?
Thanks to their specially adapted breathing apparatus, some sea snakes can stay submerged for up to two hours. They have been observed hunting as deep as 250m.
Where do sea snakes live?
Most species of sea snakes live in warm coastal waters of the Indian and Pacific Oceans. They stick to shallow water – usually no deeper than 30m – because they need to be able to reach the seabed to hunt and forage, whether in mangroves, on coral reefs, in seagrass meadows or on the sand or mud of the sea floor.
One species, the yellow-bellied sea snake, lives in the open ocean, preying on fish close to the surface. This behaviour makes it the most widely ranging snake in the world.
What do sea snakes eat?
Most sea snakes eat fish, including eels, and fish eggs, with the specifics of their diet varying by species. Two groups eat only fish eggs, while another prefers burrowing eels. Some sea snakes hunt in nooks and crannies, while others cruise along the sea bed.
Living in open water, the yellow-bellied sea snake feeds by lying motionless at the surface and grabbing unsuspecting prey fish that come to shelter beneath it.
Feeding patterns also vary: while some sea snakes are mainly nocturnal, others feed during the day and rest at night. Sea snakes use their venom to paralyse or kill the fish they catch – in some cases their venom even begins the digestive process.
How do sea snakes reproduce?
Living in the ocean for the whole of their lives, true sea snakes mate at sea and give birth to live young, typically between two and nine at a time. Sea kraits, on the other hand, are egg laying (or oviparous), so must go ashore to lay their eggs.
They mate on land too, with males thought to follow females to shore using a highly developed sense of smell. Once mating has occurred, a female will find a cave or rocky crevice in which to lay a clutch of between four and 20 eggs.
What threats do they face?
One species of sea snake, Crocker's sea snake, is listed as vulnerable on the IUCN Red List of Threatened Species, but numbers for many species are thought to be in decline.
This is down to factors including climate change, which threatens sea snake habitat due to rising sea temperatures, and the threat of bycatch, with sea snakes becoming entangled in the fishing nets of trawlers. Black-banded sea krait have historically been hunted for their meat.
Do sea snake shed their skin like land snakes?
Semi-aquatic sea kraits shed their skin in the same way as terrestrial snakes, by rubbing themselves on rocks once ashore. True sea snakes do the same thing in the water, using submerged rock or coral to loosen their old skin.
The yellow-bellied seasnake, which spends its life in open water, has had to come up with another method, however – it pulls itself into a knot, twisting and coiling to rub the old skin loose. This behaviour is useful at other times too, to rid the snake of unwanted organisms like barnacles or algae.
How long do sea snakes live?
Sea snakes can live up to 15 years, depending on species
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