Nick Baker tells all about this aquatic predator that employs odd appendages and clever tactics to disarm its fishy prey
Many species of snake, from the anaconda to the banded sea krait, have mastered the watery realm. Nothing particularly unusual in that. But there is one that has fascinated me since I first set eyes on it, in a tank in an American zoo.
Its name, tentacled snake (Erpeton tentaculatum) conjures up some pretty far out images. A snake with tentacles – how weird must that be?
The reason this snake seems never to have slithered into the public conscience is that both tentacles and the snake are not in fact as spectacular as they might at first sound. And that is all part of the point.
Inhabiting the weed-choked ponds, ditches and paddy fields of South-East Asia, the tentacled snake does a spectacular job of exactly resembling the plants of its watery home. It’s a skinny little thing, less than 75cm long and decorated with a sombre patterning of brown and grey, occasionally developing a living fuzz of algae to add to its crypsis.
In fact, the species is so well camouflaged that I spent several minutes staring at that zoo tank before its inhabitants became apparent. This is the snake equivalent of a praying mantis. Fully aquatic, it sits motionless amid the tangle of stems, waiting for small fish to blunder into its personal space.
So trusting is this creature of its camouflage, that even plucking one out of the water isn’t enough for it to break out of character. It remains stiff and unmoving.
So, about those tentacles. These are certainly not kraken-like suckered limbs that drag unsuspecting fish to their doom, rather a pair of short-scaled projections on either side of the nose, just 13mm long on an adult.
They are odd, floppy devices, and until recently they’ve had scientists perplexed. Were they lures to entice curious fish within range? Possibly. Were they further accessories to camouflage? Unlikely. As it turns out, these appendages are a highly enervated pair of directional ‘fish finders’.
The alarmed fish often swims directly into the snake’s mouth
And the best bit of their dastardly design is they have evolved to outwit a well known fish predation avoidance strategy – and even use it to their advantage. When a fish senses a troublesome movement, it deploys a reflex strategy called the ‘C-start’. In less than six milliseconds, the muscles on the opposite side of the body to the threat contract, bending the fish into an extreme ‘C’ shape. It is now ready to accelerate away from danger – but the trouble for the fish is that the snake anticipates this.
Adopting a characteristic position with its body stretched out and its head and neck partially bent backwards towards its tail, the snake waits motionless for a fish to bumble into the arc created. Once it detects the fish with its tentacles, rather than strike its head directly towards its victim, it feigns an attack with a subtle movement of the area of stretched-out body behind the head. The alarmed fish, detecting this dummy move, initiates the C-start and darts off in the opposite direction – often swimming directly into the snake’s waiting mouth.
The whole process from bluff to capture is faster than the human eye can perceive – so fast that the details of the deception have only recently been revealed using highspeed film. The game is over for the fish in less than 30 milliseconds.
Tentacled snakes are considered rear-fanged. They deploy a specific venom to rapidly subdue feisty fish via grooved teeth towards the back of the mouth.
They can switch between two equally effective sensory systems depending on the light and water conditions. When visibility is good, they can make do with just their vision, but the tentacles come into their own when it is dark or when the water is very cloudy. The snakes can accurately catch fish using either just their sight or just their tentacles.
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