The snail that surfs

Surf and turf...
03 May 2024




It’s a beautiful day here on the Atlantic shores of South Africa. Much better than that sewage plant, in any case. The nutrient rich waters around here play host to some of the most striking and impressive organisms on our planet. Great white sharks, humpback whales, seals, penguins, I could go on. All of that life, all of those natural processes will inevitably lead to a lot of… Waste. Not that kind of waste, we’re talking about something else this time. The dramatic predator prey interactions in these waters will inevitably produce detritus. Half eaten fish, even the odd whale carcass. With the right tidal forces, a very real beach like this one that I’m definitely on can become something of a buffet for scavengers. But in the world of scavenging, it’s very much first come first served, which is a problem if, for instance, you happen to be a snail.

Now obviously we’re not talking about your run of the mill garden snail that causes great heartache for my mum. The snail in question is Bullia digitalis, often known as the plough snail. It has another name too, but we’ll get to that. They’re a pretty common sight on the South African coast, growing to about 6 cm long. If you’d never seen one before, you’d be forgiven for thinking a shell had found its way on top of a flat jellyfish.

The point is, this snail is not particularly quick. Indeed, during low tide, the snail’s locomotion looks very similar to if you tried to swim breaststroke whilst tied up in a bin bag. Such is life when you only have one very wide foot. However, when the tide turns, so do the tables.

Bullia digitalis is a special snail. It took its singular foot and saw not crisis, but opportunity. Because this snail is a surfing snail.

If Bullia digitalis senses a delicious meal in the same direction that the tide is flowing, it rolls onto its side, hoists it foot up like a sail in alignment with the waves, and surfs along the sea floor towards its delicious meal.

Now it’s not quite smacking the lip of a quality nug, which are surfing terms that I’m definitely cool enough to understand, and sure it can only hang one, but it’s still very impressive. The only speed limit is the speed of the waves. This thing can fly past the scavenging competition, with crucially very little energy expenditure.

Once this gnarly gastropod has reached its dining spot, it uses a proboscis, because this snail is weird enough that only now am I getting to the bit where it has a straw, and sticks it into the carrion and sucks up the soft tissue. Delicious.

And the other advantage of having one massive sail foot? When the tide starts to go out, Bullia digitalis can just plant the foot in the sand and stop itself from being pulled out to sea.

The fact that a snail the size of a drink’s can has the wherewithal to understand that tidal forces can carry it to food is remarkable, and long may this creature continue to shred the gnar.


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