Intermediate 8 minutes
Sea snakes: potent venom, extremely rare bites
Where they live, why they almost never bite, and what to do in the unlikely case
They're among the most venomous animals in the sea, and at the same time one of the most peaceful encounters you can have underwater. Many divers have had one swim between their legs on its way up to breathe, with absolutely nothing happening.
In this article you'll see where sea snakes live and where they don't, how they behave, why bites on divers are exceptional, what's distinctive about the envenomation picture, and what first-aid measure matches this type of venom.
It's a perfect example of the difference between potential danger and real risk, which is what this whole category is about. This article is educational material and does not replace specific first-aid training or medical judgment.
Where they are and what they are
Sea snakes are reptiles related to cobras and other elapids, fully adapted to aquatic life, and already appeared in the article on marine reptiles. There are on the order of seventy species, and all of them live in tropical and subtropical waters of the Indo-Pacific: from East Africa to the coasts of the American Pacific.
The most useful geographic fact is a negative one: there are no sea snakes in the Atlantic, the Caribbean, or the Mediterranean. A diver in Cozumel, in the Red Sea (where they're also absent) or in the Canary Islands will not encounter one, and what's sometimes mistaken for one is almost always a moray eel, a garden eel, or a ribbon fish.
Within the group there are two lifestyles. Most are fully marine, with a flattened, paddle-shaped tail, and give birth to live young in the water without ever needing to come ashore. Sea kraits, by contrast, are semi-terrestrial: they come ashore to rest, shed, and lay eggs, and are found both on the reef and on shoreline rocks.
All of them breathe air, so they surface regularly. Many species can stay submerged for long periods and supplement lung breathing with gas exchange through the skin, which explains those prolonged dives while they search through crevices.
Their diet is fish, eels, and fish eggs, caught in reef holes. That's the activity a diver almost always observes: a snake poking its head into every crevice, completely oblivious to their presence.
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