The Yellow-Bellied Sea Snake: Pernicious Predator or Sissy Serpent?

A dangerous outsider recently washed onto Southern California’s shores. The visitor, likely exhausted from tossing to and fro in frigid waters, was a stranger to our land. It inspired confusion and caution in those who found it. Who was this strange alien?

A resting yellow-bellied sea snake, Hydrophis platurus. Photo by William C. Flaxington.

It was a yellow-bellied sea snake, Hydrophis platurus, delivered far from the warmer waters it prefers. This single serpent sparked a flurry of news coverage, as it was one of only a handful of its kind to arrive on a California beach since 1961. Many reporters discussed the warming waters of El Niño, the probable cause of the snake’s stranding so far north, and correctly described it as very venomous.

But no one addressed the question that likely loomed in so many minds: how dangerous is this snake exactly, and what would happen if it bit you?

I’ll answer that question in gory detail, and then I’ll explain why it would probably never happen. 

So what happens if the yellow-bellied sea snake’s venom starts coursing through your veins? Early symptoms are akin to the flu; you’ll grow nauseated, your head may ache, and you’ll sweat. Inside your body, the snake’s neurotoxic venom begins shutting down your nervous system.

The yellow-bellied sea snake’s venom contains a swirling protein cocktail. The most important proteins in that stew are pelamis toxins. Pelamis toxins shut down your nervous system by binding to neurons and stonewalling their electric signals, which blocks communication between nerves and muscles. Freeze those neurons and paralysis follows.   

Your eyelids will droop, your muscles will grow sore, and your body will start to shut down. If the venom works its way to your heart or diaphragm, you’ll die of cardiac arrest or suffocation. If you manage to survive long enough, your skeletal muscle will break down and leak the byproducts into your blood stream, which will overwork and kill your kidneys. You may live to see yourself pee blood.

But that will probably never happen. Why?

The yellow-bellied sea snake is both literally and figuratively yellow-bellied. It has beautiful banana yellow scales on its underside. It’s also timid. Like many sea snakes, Hydrophis platurus is hesitant to bite and will only strike when manhandled.

It also has a crude venom delivery system. Not all snakes bite the same way. Some are rear-fanged: their fangs sit toward the back of their mouths and are essentially hollow versions of regular snake teeth. They don’t inject; they drool. To envenomate, these snakes have to clamp down and chew. Imagine your spit was venomous. If you were rear-fanged, you’d have to bite, chew to open a wound, and drool into the gash to envenomate someone. Like I said, it’s crude.

Other snakes, like the Russel’s viper, have a more refined system. Russel’s vipers, like all vipers, have posable fangs that sit sheathed in the front of their mouths. When they strike, the fangs unsheathe and can near fully extend like a pair of outstretching hypodermic needles. The motion is more of a stab than a bite.

The yellow-bellied sea snake is somewhere between these two. Their fangs are fixed in their jaws, so they have to crudely latch on and chew. They’re also positioned toward the front of their mouths, like the viper. But their fangs are small, so even when the snake does sink them into your skin, only a small amount of venom, if any, works its way inside.

How does the yellow-bellied sea snake stack up against other venomous snakes of the world? That all depends on how you want to die. How do you feel about necrosis (essentially zombification), where cell-destroying venom dissolves your tissues until they slide off bone? Then Africa’s puff adder is your snake of choice. How about irreversible blindness? Don’t start a staring contest with any spitting cobras. Which venom is worse is all about picking your poison.

Though the yellow-bellied sea snake’s venom is indeed potent, remember that a bite is unlikely, and even if the snake did latch on, your fragile nerves would probably see little to no venom.