Reptiles
Sandfish Skink
Scincus scincus · also called sandfish skink, common sandfish
The sandfish skink does something that looks impossible — it dives into dry desert sand and swims through it, its smooth body rippling in the same S-shaped waves a fish uses in water. Buried and invisible, it can still feel an insect walking on the surface above and lunge up to catch it.
Overview
Sandfish skinks live in the sandy deserts and dunes of North Africa and the Middle East, in fine, loose, wind-blown sand. About 13–20 cm, smooth and pale yellow with a wedge-shaped snout, they hunt insects, larvae, and spiders.
Swimming through sand
It flattens its legs against its body and propels itself with side-to-side body waves, moving a few centimetres below the surface exactly as a fish swims through water.
A body sealed against grains
A recessed jaw, polished scales, valve nostrils, and sealed ears keep sand out, and it senses prey through ground vibrations while completely buried.
Status
The sandfish skink is Least Concern, widespread and common in suitable sandy desert across its large range.
Sandfish Skink: common questions
Does the sandfish skink really swim through sand?
In a functional sense, yes. When it enters loose, dry sand, the sandfish skink presses its short legs back against its body and propels itself forward using rhythmic side-to-side waves passing down its smooth body and tail, the same lateral undulation that fish use to swim and that eels use to move through water. High-speed X-ray studies of sandfish moving through sand have shown that below the surface the animal behaves much like a swimmer, with the sand fluidising around it as it moves, so the description of it swimming through sand is more than just a metaphor. It typically travels a few centimetres to tens of centimetres below the surface.
What adaptations let the sandfish live inside sand?
The sandfish has an unusually complete set of features for a life spent moving through and buried in sand. Its head is smoothly wedge-shaped for entering the sand cleanly, its lower jaw is countersunk beneath the upper so that grains are pushed aside rather than forced into the mouth, and its scales are exceptionally smooth and hard, which reduces friction and wear as it moves. Its nostrils have valves, its eyes have protective lids, and its ear openings are covered by scales, all of which keep sand out, and its toes bear comb-like fringes that help it push against loose grains when it does move on the surface.
How does the sandfish find food if it is buried?
While it lies just under the surface, the sandfish is highly sensitive to substrate-borne vibrations, and it uses this to detect insects and other small invertebrates moving on or near the sand above and around it. When it senses suitable prey close by, it can burst up out of the sand, seize the insect, and either eat it at the surface or pull it back under. This ambush-from-below strategy lets the skink hunt effectively while staying hidden from its own predators and out of the lethal daytime heat, only needing to expose itself for the brief moment of the strike.
Why is the sandfish skink of interest to engineers?
The sandfish has become a model organism for researchers studying how animals move through granular materials like sand, which behaves in complex ways that are neither fully solid nor fully liquid. By filming and X-raying sandfish as they burrow and using the data to build physical and computer models, scientists have gained general insights into the physics of movement through loose grains. That work has fed into the design of robots intended to move through sand, soil, or rubble, for example for search and rescue or planetary exploration, making the small desert lizard an unexpected reference point for robotics.