Some lizards swim through sand as though it were water. Why?

Oct 03, 2019

AFICIONADOS OF “Dune”, Frank Herbert’s novel about a planet covered by Sahara-like desert, will be familiar with the idea of animals that swim through sand. Giant worms which do just that are a feature of the book. Back on Earth, though, there are sand-swimmers, too. And these ones are real. At least eight groups of lizards have a habit of diving headfirst into sand, if it is available, and making paddling motions with their limbs to carry them below, as if they were submerging themselves in a body of water. The question is, why?

Obvious hypotheses include evading predators and controlling body temperature. However, Ken Toyama of the University of Toronto has a third: that the animals are ridding themselves of skin parasites. And he has data to back his theory up.

Skin-grooming, which is crucial to any vertebrate’s health and hygiene, can be a struggle for lizards. The layout of their skeletons means they cannot rotate their heads around far enough to reach certain parts of their bodies, in order to nibble parasites away. Nor, for want of the neural apparatus needed to keep track of favours given and received, can they easily play the mammalian game of “you scratch my back and I’ll scratch yours”. These facts, plus recent research conducted in the scrublands of Florida, which showed that a sand-swimming lizard species...

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