The sandfish lizard wriggles through desert sands like a sci-fi monster.
Now, using computer simulations and bendy robots, researchers at
Georgia Tech in Atlanta have taken the most complete look yet at the
everyday physics of burrowing animals. And, boy, does this reptile
wriggle, the team reports online February 23 in the Journal of the Royal
Society Interface. “This particular behavior is built for speed,” says
physicist Daniel Goldman, one of the study coauthors.
Like the
deadly sandworms in the Dune science fiction series, a host of animals
from scorpions to snakes haunt subterranean deserts across the planet.
It’s not easy to study how these creatures careen through their
environments, Goldman says. Scientists have a good idea how water
behaves in the wake of an undulating eel or how air flows over a bird
wing. But shuffling sand grains ping off each other like a wickedly
complicated game of pool.
X-ray studies have shown that sandfish
lizards (Scincus scincus) navigate such chaos with a wormlike
wriggle, Goldman says, tucking in their legs and curling from side to
side in S-shaped waves. A fast sandfish lizard dive covers two body
lengths per second — and the creatures can grow to 4 inches long, he
adds. But just how the lizards achieve such speed in a complex sandy
environment wasn’t clear. For that, Goldman’s team turned to a new set
of tools.
First, researchers simulated sandfish lizards swimming
through a field of 3-millimeter-wide glass beads on a computer. The
program — which ate up 20 to 30 desktop PCs and still took days to run —
illustrated how every bead bumped and thudded as the virtual lizard
passed by. The real fun came next. The team built a spandex-covered
robo-reptile that could wriggle much like the real thing. “The beauty of
robotics compared to the simulation and theory: It’s all in the real
world,” Goldman says. If the team wanted the robot to bend more or less,
the researchers just asked it to bend more or less.
On-screen or
clad in spandex, the tests agreed. If virtual lizards curl too much,
they don’t move far enough forward with each wriggle. If they bend too
little, the lizards can’t give enough push. Real-life sandfish lizards
walk, or wriggle, this fine line nearly perfectly. “They dive into the
sand as fast as they can,” Goldman says.
Such finely tuned diving
isn’t useful just for lizards, says Robin Murphy, director of the
Center for Robot-Assisted Search and Rescue at Texas A&M University
in College Station. She designs robots to help in the aftermath of
disasters like earthquakes or mudslides. But when it comes to machines
that can dig like earthworms and slip through rubble, nothing like that
exists, she says. “There’s a lack of any technology short of a shovel.”
Burrowing animals could inspire new machines, but so far, few studies
have been able to capture the constraints robots would face in
dirt-filled or muddy environments. “This is the first I’ve seen that I
said, ‘Okay, we’ve got it,’” she says.
Robots inspired by
animals are neat, admits Eric Tytell, a researcher at Johns Hopkins
University who studies how fish swim in water. But the Georgia team
flipped that inspiration around, too. Goldman and his colleagues used
robots to get a better grasp of biology. And that’s really clever,
Tytell says.
Goldman says his studies have convinced him that
sandfish lizards dive for one reason — to escape. In the desert, there’s
nowhere else to hide. “You just want to get the hell out of there as
fast as you can,” he says.
Quick getaway from Science News on Vimeo.
Sandfish lizards native to the Saharan desert may dive deep to get away from predators.
Credit: Ryan Maladen, Yang Ding, Paul Umbanhower, Adam Kamor, Daniel Goldman/Georgia Institute of Technology.
A desert dive from Science News on Vimeo.
Sandfish lizards swim through sand by tucking in their legs and wriggling their bodies, not unlike some worms.
Credit: Ryan Maladen, Yang Ding, Paul Umbanhower, Adam Kamor, Daniel Goldman/Georgia Institute of Technology
