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Sea snakes are a group of marine reptiles that have captured the curiosity of scientists and nature enthusiasts alike due to their exceptional adaptations to living in saltwater environments.
Comprising seven genera and up to 69 species, which include the sea kraits and true sea snakes, these animals have evolved a range of fascinating traits such as potent venom, paddle-shaped tails, and the ability to hold their breath for extended periods.
Despite being closely related to cobras, sea snakes have established their unique place in the ocean, with the Belcher’s sea snake holding the notoriety of being the most venomous and perilous of them all.
Distribution & Habitat
The only place that sea snakes are not found is in the Atlantic Ocean. Other than that, they’re abundant all over the world, particularly in the Indian and Pacific Oceans. The question of why they’re not found in the Atlantic has baffled scientists for many years and there are a couple of theories as to why this is.
Some suggest that cold currents from Namibia are to blame for the lack of sea snakes, whereas others think that it’s merely to do with the fact that sea snakes cannot access the Atlantic. Due to land blocks and the need to travel through colder waters to get to the Atlantic, the snakes simply cannot get there.
They prefer warm tropical waters from the east coast of Africa right down to the northern part of New Zealand. Around the Americas, they are common in the Gulf of Mexico.
In terms of habitat, sea snakes generally prefer to stay in shallower waters, but there are instances where they may be found a little further out. They’re common in estuaries and sheltered areas as well as mangroves. While there are some brackish species, this isn’t as common, although when sea snakes swim up rivers, they can often end up miles from the ocean.
Sea snakes have thin, sharp teeth that allow them to catch their prey before swallowing them whole. Generally, these snakes will eat various species of fish, but they’re also known to feed on crustaceans, mollusks, and fish eggs. Their favorite food appears to be eels!
However, they’re not at the top of the food chain and are predated by large fish and sharks, sea birds, and even crocodiles in some areas.
Reproduction & Lifecycle
Sea snakes give birth to live young. This is something that’s sometimes seen in terrestrial snakes, but in the ocean, the sea snake is the only reptile that does this. This is mainly true of true sea snakes, who cannot go up onto land to lay their eggs. However, some species of sea krait will leave the water to lay.
Not a lot is known about the mating rituals of sea snakes, although there is the suggestion that large schools may come together during the breeding season.
When the young are born in the water, it’s possible for them to be almost as large as an adult, and in a clutch, there could be between three and four young. However, some records show females giving birth to more than 30 young at once!
Sea Snake Adaptations
It’s thought that sea snakes have been evolving for more than 15 million years, so it’ll come as no surprise that they’ve developed some pretty unique adaptations during that time. With adaptations to their vision and ability to live in a saline environment, they’re perfectly suited to life in the ocean.
Salt Glands & Special Nostrils
Living in the sea means that snakes swallow a lot of salt water. This cannot be avoided, so the snake needs a way to get rid of any excess salt from their bodies while still taking in water for hydration.
For this, they have a special gland underneath their tongue that allows them to get rid of the excess salt. All the snake needs to do is flick its tongue, and the salt is expelled through the mouth.
Hydrodynamic Body Shape
The scales of a terrestrial snake overlap one another, but in sea snakes, this would make them less hydrodynamic. Instead, they have smooth scales that allow them to glide through the water.
What’s more, the tail of a sea snake is flattened and often described as ‘paddle-like’ which aids in smooth movement.
You’ll also notice that the body of a sea snake is more elongated and streamlined compared to that of a land snake.
Some Have Gills
A lot of sea snakes need to come to the surface to breathe. However, there are a few species, such as the annulated sea snake, that have gills and so can remain underwater for a much longer time.
These gills are made up of a series of blood vessels that draw in oxygen and are located around the forehead and the snout. They work in a similar way to the gills of a fish.
The light conditions in the ocean have changed greatly over the course of the 15 million years that sea snakes have been around. To continue hunting for prey and staying on the lookout for predators, these snakes have had to adapt their vision. In recent studies, it’s been noticed that the vision of sea snakes has been genetically modified over millions of years to include the ability to see in color.
This suggests that, before these snakes entered the ocean, they were once terrestrial animals, and these adaptations have helped them fit into their new environment.
Sea snakes need to stay submerged for quite some time when hunting, and this means being able to hold their breath for a long time. Having a regular set of lungs wouldn’t buy them enough time underwater, so sea snakes have a single, elongated lung, that’s almost the same size as their entire body!
What’s more, a lot of sea snakes are able to absorb oxygen through their skin, allowing them to remain submerged for longer.
Are Sea Snakes Venomous?
There are seven genuses of sea snakes, and all of them apart from one, emydocephalus, are venomous. Their venom contains a mixture of myotoxins and neurotoxins, and in many cases, is more potent that the venom of their cobra cousins.
It is rare that humans will encounter sea snakes owing to their ocean habitat. However, when they do, bites are not common, and even when they do occur, the snake doesn’t usually inject venom. While the bite may not be initially painful, it’s not uncommon for the teeth to remain, so these need to be carefully extracted.
In the event that the snake does inject venom, you might not notice any signs for at least half an hour. Symptoms can be mild, including things like headaches, nausea, sweating, and pain, or they can be more severe with things like paralysis. In some cases, a bite from a sea snake can be fatal, but this typically only happens when the breathing or swallowing muscles are affected.
Sea Snake Species
With around 69 species of sea snakes in our oceans, there’s lots of diversity. I’d like to introduce you to some of the world’s most interesting sea snakes.
1. Banded Sea Krait (Laticauda colubrina)
Found in the western Pacific and eastern Indian Oceans, the banded sea krait is the most widely distributed sea snake within its family. It’s so abundant that it’s not listed on any database as being endangered or threatened.
These snakes are found in coastal areas and possess a potent neurotoxic venom that can be dangerous to humans. They hunt for prey alone but are often seen coupling up with goatfish for a more effective outcome.
Banded sea kraits have a black head with yellow markings around the eyes and the upper lip, which is why they’re sometimes called the yellow-lipped sea krait.
2. Yellow-Bellied Sea Snake (Hydrophis platurus)
The yellow-bellied sea snake, as you might imagine, is yellow on the underside but has a distinct black upper side and markings on its paddle-shaped tail. They’re common snakes that are considered to be endangered.
These snakes are found in the Indian and Pacific Oceans from east Africa to Southeast Asia and across to Baja, California. Out of all sea snakes, the yellow-bellied sea snake can be found furthest out into the open ocean although there have been a few reports of individuals in mangroves, but this is rare.
Yellow-bellied sea snakes have a neurotoxic and isotoxic venom but they rarely come into contact with humans. Instead, they’ll spend their days foraging for fish.
3. Olive Sea Snake (Aipysurus laevis)
The olive sea snake, despite its name, is actually brown to purple in coloration along the back. These snakes typically grow to around 39 inches (100 cm) although some individuals can be double that size.
They’re often encountered by humans as the snakes swim around looking for prey like crustaceans and fish. While they are venomous, they’re not typically aggressive to humans. When hunting, they can spend up to two hours under water, but adults usually resurface to breathe every 30 minutes.
Olive sea snakes are very common around the tropical coasts of Australia, particularly around the Great Barrier Reef. They tend to stay in shallower waters but can dive to around 230 feet (70 meters).
4. Dusky Sea Snake (Aipysurus fuscus)
The dusky sea snake is an endangered and therefore protected species across its entire range, which covers the shallow reefs of the Timor Sea.
These are brown/purple colored snakes that hand light banded markings along the body and don’t typically grow much larger than around 12 inches (31 cm).
Dusky sea snakes hunt for wrasses and gobies around the coral reefs. However, one of the main reasons for their decline is habitat loss. Still, it’s thought that individuals could live as long as ten years in the wild.
5. Dubois’ Sea Snake (Aipysurus duboisii)
The Dubois’ sea snake is found in the waters that surround Australia, Papua New Guinea, and New Caledonia and is one of the most highly feared sea snakes due to how toxic its venom is. These snakes are considered to be one of the most venomous sea snakes and the third most venomous snake overall.
Dubois sea snakes, sometimes called the reef shallow snake, are moderately aggressive but usually only bite when threatened. The females give birth to live young and individuals will feed on fish as well as moray eels.
While the range of these snakes is not huge, the species is considered to be of least concern by the IUCN Red List. However, it is thought that numbers in the wild are decreasing.
6. Stokes’s Sea Snake (Hydrophis stokesii)
Stoke’s sea snakes are largely found in the waters around Southeast Asia however, they can sometimes be found in the tropical regions off the coast of Australia. One of the most awesome sights is during the migration of these snakes when thousands of individuals are seen moving through the water.
The Stokes sea snake has the longest fangs of any sea snake and is a very heavy-set animal. But while the fangs are large, and these aggressive snakes are venomous, no humans have been killed by a bite.
7. Black-Banded Sea Krait (Laticauda semifasciata)
Sometimes called the Chinese sea snake, the black banded sea krait is found throughout many parts of the Pacific Ocean and inhabits coral reefs. It is most commonly found around Taiwan, Indonesia, The Philippines, and the Ryukyu Islands.
The species is venomous but is not typically aggressive to humans unless it feels threatened. They’re relatively large snakes that can reach a maximum of 67 inches (170 cm) and have a triangular-shaped, broad head with banded markings along the body.
Like many species of sea krait, the black-banded sea krait does not give birth to live young. Instead, the females lay between three and seven eggs in a clutch.
8. Annulated Sea Snake (Hydrophis cyanocinctus)
The annulated sea snake is a particularly interesting species as it has a feature that allows it to take in oxygen. This feature is in the form of a hole on the head which contains a large blood vessel for taking in oxygen while the snake is underwater.
Annulated sea snakes are a species of true sea snake, and the females give birth to live young. They’re usually around 4.9 feet (1.5 meters) as adults, but there are records of much larger specimens reaching almost 9.8 feet (3 meters) in length!
These snakes are mainly found in the Indian Ocean and are highly venomous with a venom that contains neurotoxins. While the snakes aren’t aggressive, they may bite if threatened, and although the bite isn’t painful, the venom could be enough to cause a fatality.
9. Turtle-Headed Sea Snake (Emydocephalus annulatus)
The snout of the turtle-headed sea snake is pointed and hard, just like that of a turtle which is where the snake takes its name. These snakes are found in the Indian Ocean around the Philippines and Indonesia, as well as the Northern coasts of Australia.
Turtle-headed sea snakes spend most of their time around coral reefs where they can be found hunting for fish eggs. This is its main source of nutrition and damselfish eggs are the snake’s primary target.
While the turtle-headed sea snake is listed as being of least concern, there has been a decline in its numbers in some regions such as around New Caledonia.
10. Horned Sea Snake (Hydrophis peronii)
An abundant species within its range, the horned sea snake is found around the coasts of Australia, Indonesia, Taiwan, Thailand, the Philippines, and New Caledonia. These are very unique-looking sea snakes with a spiny head, the snakes grow to around 4 feet (1.2 meters) in length.
Horned sea snakes have the appearance of a dragon and spend their time waiting for unsuspecting gobies to pass by before ambushing them.
Sometimes called the Peron sea snake, these animals give birth to live young, with females producing up to ten young at once.
11. Olive-Headed Sea Snake (Hydrophis major)
You may sometimes hear the olive-headed sea snake being referred to as the greater sea snake. This species is found around New Caledonia, New Guinea and some parts of the tropical Australian coastlines.
The greater sea snake is yellow to brown in color and has dark markings across the back. It’s a mid-sized snake that tends to grow to just over 3.5 feet (1.1 meters) in length.
These snakes are venomous but are generally not aggressive toward humans. The only time that they may display heightened aggression is during breeding season, when they may seemingly attack for no reason.
12. Beaked Sea Snake (Enhydrina schistosa)
The beaked sea snake has a dark coloration along the back with a lighter underbelly and sides. Younger specimens may have dark-colored bands and be more olive in color. This species can grow anywhere between one and 6.6 feet (2 meters) in length.
Out of all sea snakes, the beaked sea snake is responsible for the largest number of bites on humans as well as causing more fatalities.
The snake takes its name from the hooked scale on the front of the nose, which gives the appearance of a beak.
They’re found around the coasts of India and as far south as Australia. Within their range, they are one of the most common sea snake species, and there is no concern about them becoming endangered.
13. Elegant Sea Snake (Hydrophis elegans)
The elegant sea snake is found around all of the Australian coastlines apart from the south, although it has been seen around the island of Tasmania. They are medium-sized snakes that usually grow to around 79 inches (2 meters) in length and are relatively slender compared to some sea snake species.
Elegant sea snakes have a special adaptation that allows them to close their nostrils to prevent water getting inside as they submerge themselves. Unlike a lot of sea snakes that tend to remain closer to the surface, the elegant sea snake has been recorded at depths of up to 475 feet (145 meters). That said, they are often seen along shores and in lagoons.
These snakes possess a neurotoxic venom which can cause problems in humans that range from fatigue to total paralysis.
14. Belcher’s Sea Snake (Hydrophis belcheri)
While some believe that the Dubois sea snake is the most venomous, it’s actually the Belcher’s sea snake that holds this title. Its venom is 100 times more potent than any land snake but the good news is that it rarely attacks humans and when it does, it’s not just for the sake of it. What’s more, when they do bite, they often don’t release much, if any venom so bites are rarely fatal.
The Belcher’s sea snake is found all over the Indian Ocean and has the special ability to remain underwater for as long as seven to eight hours. This benefits the snake when hunting, and it will even sleep underwater before coming up for air.
15. Blue-Lipped Sea Krait (Laticauda laticaudata)
One of the most distinct and beautiful looking sea snakes is the blue-lipped sea krait with contrasting black and blue rings around its entire body. However, looks can be deceiving as this is an extremely venomous snake that delivers a neurotoxin capable of causing respiratory failure, paralysis, and even death.
Sometimes called the blue-banded sea snake, this species lives in the Indian Ocean and parts of the western Pacific and can grow up to 3.3 feet (1 meter). However, the females are typically a little larger than the males.
While the snakes spend most of their time alone, they will gather in large numbers on the shore during the breeding season.
16. Short-Nosed Sea Snake (Aipysurus apraefrontalis)
The short-nosed sea snake is considered to be critically endangered. At one point, it was believed that the snakes were extinct as they had not been documented for decades. However, recently, they were rediscovered in Australian waters, where they are endemic.
It’s thought that there are many reasons for the snake’s decline. One of these reasons is how slow the short-nosed sea snake is to breed. Other reasons include warming sea temperatures and trawling.
Short-nosed sea snakes are found around coral reefs and only occupy an area of around 3.9 sq miles (10 sq km). They are brown in color and generally grow to around 24 inches (60 cm) in length.
These snakes are venomous, but this is mainly used when catching prey which includes eels and gobies.
Can Sea Snakes Survive on Land?
There are two types of sea snakes; sea kraits and true sea snakes. While sea kraits can survive on land, true sea snakes cannot. The main reason for this is that true sea snakes do not have suitable anatomy that makes it possible for them to move on land. Even with sea kraits, their terrestrial movement is limited and nowhere near as free as a land snake.
Where land snakes have ventral scales, this is not a trait seen in true sea snakes which is what makes it difficult for them to move on land. However, while these scales are small or absent in sea snakes, they are present in sea kraits, which means that these animals are not only able to move on land but can also climb.
Sea Snake Venom Toxicity
Most sea snakes are highly venomous, but the number of bites delivered to humans are so few that these snakes pose no real danger to us. Yes, there are reports of fatalities from sea snake bites, but these are incredibly rare. What’s more, owing to the lack of bites, there are very few antivenins available for sea snake bites. That said, there is one that’s regularly produced in Australia.
Sea snakes are largely docile creatures that only bite when they feel threatened. The bites are often painless, and in most cases, the snake will not envenomate its victim, so humans usually get away with some soreness which develops around thirty minutes post-bite.
However, if you were unlucky enough to be envenomated by a sea snake, the symptoms could range enormously depending on the species and how much venom was injected.
Sea snakes have a mix of myotoxins which affect the muscles as well as neurotoxins which affect the nervous system. When envenomated, one may experience pain or stiffness in the muscles, and in severe cases, paralysis may occur.
Other symptoms of a sea snake bite can include swelling, respiratory failure, fatigue, dizziness, and in the worst cases, death.