These Invasive Snakes Twist Their Bodies Like Lassos To Climb High

The movement is how brown tree snakes have devastated the native birds on Guam.

a brown tree snake
Brown tree snakes are believed to have destroyed much of Guam's bird population.

Bjorn Lardner / USGS

Snakes don’t just slither. For the past century, those who study snake movement have documented that snakes move in four ways: rectilinear, lateral undulation, sidewinding, and concertina.

But researchers have uncovered a new type of snake movement that lets the invasive brown tree snake climb tall, smooth cylinders in a way they never knew before. They call the movement lasso locomotion in a new study in the journal Current Biology.

Researchers made the unexpected discovery while working on a project targeted at protecting the nest of Micronesia starlings. The birds are one of only two native forest species that still remain on Guam.

“The brown tree snake has decimated native forest bird populations on Guam. The snake was accidentally introduced to Guam in the late 1940s or early 1950s,” lead author Julie Savidge, emeritus professor at Colorado State University, tells Treehugger. “Shortly thereafter, bird populations started to decline.”

Savidge conducted her doctoral work in the 1980s and identified the brown tree snake as the reason the birds were gone.

"Most of the native forest birds are gone on Guam," she says. "There's a relatively small population of Micronesian starlings and another cave-nesting bird that has survived in small numbers. The starling serves an important ecological function by dispersing fruit and seeds which can help maintain Guam's forests."

To protect the birds, researchers were using a three-foot long metal baffle to try to keep brown tree snakes from climbing up to bird boxes. The same baffles have been used by birdwatchers to keep other snakes and raccoons away from bird boxes.

But researchers discovered that they were little impediment to the brown tree snake. They watched on video as the snake first were confounded by the baffles then managed a workaround. They formed their bodies into a lasso-like shape and wriggled up the cylinder.

“My research collaborators nearly fell out of their chairs when they first saw the lasso locomotion,” Savidge says. “I thought it was amazing when I first saw what was happening and how the snakes scaled these cylinders.” 

Lasso Locomotion

Researcher and coauthor Bruce Jayne, professor of biological sciences.at the University of Cincinnati, describes the motion.

“The snakes make a loop that completely encircles and squeezes the cylinder. Then, little bends from side to side within the loop allow them to advance upward,” he tells Treehugger.

Normally, snakes using concertina locomotion to climb steep smooth surfaces like branches or pipes, Jayne says. They move by bending sideways in order to grip at least two regions of the surface.

But with this newly described lasso locomotion, the snake utilizes the loop it forms with the lasso to create a single gripping area.

“Theoretically this pattern of movement allows these snakes to climb cylindrical surfaces more than twice the diameter of those than when using any other type of snake locomotion with gripping modes,” Jayne says.

“Thus, they can go places that would otherwise be inaccessible and potentially exploit a greater range of resources.”

Researchers say they anticipate the discovery may help ending up saving bird lives.

"Hopefully what we found will help to restore starlings and other endangered birds, since we can now potentially design baffles that the snakes can't defeat," says Savidge. "It's still a pretty complex problem."

View Article Sources
  1. "Snake Locomotion." Robinson Library.