Nature
PUBLISHED
How can a snake be right-handed? It’s a question that’s plagued this writer for the time it took to read the 2007 study, “Right-handed snakes: convergent evolution of asymmetry for functional specialization”.
It showcased the curious feeding habits of Iwasaki's snail-eater (Pareas iwasakii), a reptile that does exactly what it says on the tin. As a snail-eating specialist, it evolved to feed on snails straight out of the egg. Thing is, it can’t do it from any old direction.
Pop the skull of one of these snakes under an x-ray and you’ll notice something curious. It has asymmetry in its dentition, with more teeth on the right mandible than it has on the left. So why would a snake favor its right side over its left? Turns out, it’s a trend set by snails.
Did you know that the vast majority of snails coil their shells to the right? Strange, but true, bar a few rare exceptions (who could forget Jeremy, the left-leaning snail’s lifelong pursuit to find love?).
To test the theory that right-handed snails led to right-handed snakes, scientists conducted feeding experiments with four Iwasaki's snail-eaters. They were offered snails that coiled to the right and snails that coiled to the left, as dinner options.
The researchers’ observations revealed that the snakes were much better at eating snails that coiled to the right. They could eat them faster and needed to make fewer jaw movements to eat them in comparison to when eating the snails that coiled to the left. So bad were they at striking the left-handed snails that these ones often escaped (which, experimentally, was defined as a snail that was still alive 1 week after the initial predation attempt – humiliating stuff for the snake).
The research demonstrated why having lopsided skulls with more teeth on one side than the other is actually a big benefit for these snail-eating snakes. However, in the same breath it demonstrates how coiling to the left could be a defensive advantage for snails.
This is supported by another study that came out in 2006 that found crab scars on snail fossils that revealed how the lefties were more likely to survive than the righties. So, while lefties like Jeremy may struggle in the bedroom, it just goes to show that being different can come with some serious benefits.
And what do you know? There's a new left-leaning snail in town.
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