The truth about sea snakes & their epic venom

There are snakes and then there are sea snakes… ya feel? I’m just fascinated by them. I find it so incredible that millions of years ago a bunch of snakes began to ditch their land-loving ways and over time adapted so successfully to life in the ocean.

There are, broadly speaking, two groups of sea snakes: sea kraits (Laticaudinae) who travel between land and sea and the true sea snakes (Hydrophiinae) who live their whole lives in the ocean. All are venomous and all share a common ancestor with some of Australia’s land snakes, suggesting we’re the very continent that originally birthed ’em. You’re welcome world.

But no really, you are welcome. Because sea snakes are truly incredible creatures, still shrouded in mystery and incorrect information. Consequently, today, I’m ’bout to bust some myths on sea snake behaviour, their venomous bites and the fangs that inject them. Join me! And let me know your own experiences with sea snakes in the comments below.

A banded sea snake. Photo: Flickr/Klaus Stiefel

Just how venomous are sea snakes?

Sea snake venom is some of the most toxic venom known, not just amongst snakes but the entire animal kingdom. It’s estimated one drop (approximately 0.03 mL) of sea snake venom could kill three people, with some sea snakes capable of ousting 7-8 drops in a single bite. Consequently, sea snakes are generally considered more venomous than land snakes, with a level of toxicity rivalled only by Australia’s own terrestrial elapid snakes (such as the Taipans, Oxyuranus).

Can they bite us?

Yes. Sea snakes have front-facing, fixed fangs and bites to people can occur anywhere on our bodies. I’ve read reports of sea snake bites to fingers, toes (including the big toe), arms, face and even a scrotum!

Sea snakes do have shorter fangs than many land snakes however, ranging from just 0.6 mm to 4.2 mm in length. Therefore if you’re wearing a thick wetsuit they’re unlikely to be able to penetrate it.

But just how dangerous are sea snakes to us?

Not very!

I could find no reported deaths from sea snakes in Australia despite us having the greatest diversity of sea snake species in the world, with 32 species in our waters. Also, since 1961 sea snake anti-venom has been available which can help dramatically speed up recovery time and prevent death in most serious cases. Additionally, if sea snake anti-venom is unavailable tiger snake (Notechis scutatus) anti-venom can also be effective.

But perhaps most surprising, is that most cases of sea snake bites require no anti-venom at all! The vast majority of sea snake bites are ‘dry bites’, where no venom is injected, or bites where so little venom is injected that victims feel minimal pain and recover in a few days without the aid of anti-venom.

Consequently, the percentage of serious bites is estimated to be as low of 22%! Even in these serious cases, sea snake anti-venom is usually effective. One paper reported that in 10 cases of serious sea snake poisoning, eight survived after being administered the anti-venom, while the two fatalities could have possibly been avoided if a higher dose of anti-venom was used.

Prior to the availability of sea snake anti-venom, these rare, serious sea snake bites were more concerning. The same paper reports that around 50% of patients with serious sea snake bites died prior to 1962 (before the anti-venom became available).

A diver snaps a large banded sea snake. Photo: Flickr/Klaus Stiefel

Which sea snake species is most dangerous to people?

As above, sea snakes typically pose little threat to us, but there is a species that commonly meets with humans and has consequently caused the most cases of venomous bites.

The beaked sea snake (Enhydrina schistosa) is found around southern Asian coastlines, as well as those around Sri Lanka, India, Pakistan and Iran. Of 101 investigated sea snake bites, one study found the beaked sea snake was responsible for over half, including seven of the eight that resulted in death.

The victims of its bites were usually fisherman trying to remove the snake from fishing nets or disturbing them while wading through the water.

A beaked sea snake washed ashore. Photo: Flickr/Roy Grimwood

Finally, why are sea snakes so venomous?

Moving from land to sea has seen sea snakes take on many amazing adaptations and their epic venom is just one of them! Living in the ocean means prey is usually fast, slippery and able to escape in any direction. Consequently, sea snakes have needed to produce a highly toxic venom, able to almost instantly immobilise and kill their prey to ensure it cannot escape.

To create such a toxic venom sea snakes have kept it simple.

Many land snakes have venom that includes two things: neurotoxins (toxins that destroy nerve tissue and can consequently kill) and enzymatic components (stuff to help break down and digest their often large, bulky prey).

Alternatively, sea snake venom contains more neurotoxins and fewer enzymatic material. As sea snakes most commonly eat eels and other fish, their prey is usually slippery and cylindrical and generally easier to swallow. It’s therefore more worthwhile to invest in venom that is extremely lethal to their prey than venom that also helps to digest it.

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Kularatne, S. A. M., Hettiarachchi, R., Dalpathadu, J., Mendis, A. S. V., Appuhamy, P. D. S. A. N., Zoysa, H. D. J., … & de Silva, A. (2014). Enhydrina schistosa (Elapidae: Hydrophiinae) the most dangerous sea snake in Sri Lanka: Three case studies of severe envenoming. Toxicon, 77, 78-86.

Lukoschek, V., Beger, M., Ceccarelli, D., Richards, Z., & Pratchett, M. (2013). Enigmatic declines of Australia’s sea snakes from a biodiversity hotspot. Biological Conservation, 166, 191-202.

Mackessy, S. P., & Tu, A. T. (1993). Biology of the sea snakes and biochemistry of their venoms. Toxin-related Diseases: Poisons Originating from Plants, Animals and Spoilage. New Delhi: Oxford & IBH Publishing Co, 305-51.

Reid, H. A. (1975). Antivenom in sea-snake bite poisoning. The Lancet, 305(7907), 622-623.

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