Ottawa, August 31, 2026 - An international team led by Canadian researchers has found evidence for why snake embryos form a curious spiral. This ability to coil in the embryo is why snakes are able to hatch with the longest body of all vertebrate animals.
The study, published today in the journal Current Biology, reports that snake embryos coil into a right-handed spiral as their long body grows while being tethered by the gut. "It's like when you adjust the length of a strap and the longer, buckling side of the loop twists," explains senior author and team leader Dr. Tetsuto Miyashita, evolutionary biologist at the Canadian Museum of Nature.
"There is a touch of mystery to spirals and we are only beginning to understand how these shapes are produced in animals, such as our looping intestine, snail shells, and now these beautifully coiled snake embryos," says lead author Alexandra Weber, now a graduate student in zoology at the University of British Columbia.
Adds Miyashita: "These puzzles beckon our curiosity. After all, spiral forms in nature have inspired human creations ranging from rotini pasta, to a barber's pole or even portrayals of the biblical 'Tower of Babel'."
Solving the mystery of coiling snakes was born out of the COVID-induced lockdown in 2020. Miyashita recalls being in his home office, trying to come up with a research project that his students could do without going to the lab or museum. "Then the lightbulb turned on. I had inherited from my PhD advisor this fascination with asymmetries in animal forms. So every time I saw images of snake embryos in papers, I wondered whether they are right- or left-handed in their coiling."
With this idea in mind, Miyashita instructed Weber, then at Carleton University, and two other undergraduate students at the University of Ottawa, to send emails and hunt for pictures of snake embryos in the literature and in databases of museum collections. "We obtained pictures for more than 900 embryos from 39 snake and other limbless squamate species. That's a statistically robust sample."
The team observed that for the first few weeks of the eggs being laid, snake embryos seem only to coil dextrally, or right-handed, from head to tail. "At these stages, the embryos don't have muscles to move with, so different forces are making them coil right-handed," Weber explains. "But we didn't know what's making them do that."
To solve this puzzle, Dr. Raul Diaz, their collaborator at California State University Los Angeles, put snake embryos to a CT scan and made an interesting observation.
"Raul's CT scan of a snake embryo revealed a structure we had never seen before ¾ it was a pillar of gut stretching through the spiral of the coiling body," Miyashita says. "There's an intestine detached from the rest of the body, surrounded by tendrils of blood vessels from the yolk."
That was the moment when the team figured out why the embryos coil.
To grow a long body, snake embryos accelerate the body growth, but the gut cannot catch up with it. "So they detach the slow-growing gut, which is now tethering the lengthening body. The body buckles and twists into coiling," Miyashita explains. "This coiling force is directed so the embryos grow to the opposite side of the yolk. And the yolk is always to the left side of the embryo, hence the embryo will always start coiling right-handed."
The embryos eventually reposition themselves because they grow larger as the yolk becomes reduced. The muscles also mature so they can wiggle. "Some remain in right-handed coils, but some recoil to the left side," Weber says. "So half of these near-hatching embryos are right-handed and the other half left-handed."
To Miyashita, the new paper in Current Biology represents serendipity from a crisis. "Scientists have long been fascinated with how and why snakes evolved their strange body form. To answer that question, they tended to take a deep dive into sophisticated genetic research, looking at Hox genes, enhancers, and so on," he says. "These are key discoveries. But here, out of the COVID lockdown, we uncovered a snake's secret with a startlingly simple approach—just scroll through an album of snake embryos and record which way they are coiled, and take a good look at their anatomy."
"We are now opening the possibility to develop this model further to explain other spiral forms in nature," he adds. Weber agrees: "This all started out with a curiosity to see if snakes are 'handed'. It was exciting to follow it to deep insights about their evolution."
The study team consists of scientists, students, and professors from the Canadian Museum of Nature, the University of British Columbia, Carleton University, the University of Ottawa, California State University Los Angeles, and the University of Helsinki.
