Long before a snake can slither, it has to fold itself into an egg — and a new study says it does so in a strikingly consistent way. Researchers led by the Canadian Museum of Nature report that snake embryos overwhelmingly coil in a right-handed spiral in the early stages of development, and they say they have finally figured out why.
The team, led by University of British Columbia researcher Alexandra Weber and the museum's Tetsuto Miyashita, examined more than 900 embryo specimens spanning 39 species of snakes and other limbless squamates, using CT scans to map the hidden anatomy inside eggs, according to an EurekAlert release tied to the study, published Aug. 31 in the journal Current Biology. In the earliest stages, before the embryos have developed working muscles, coiling is almost exclusively right-handed; by the time embryos are near hatching, the split evens out to roughly half right-handed and half left-handed.
The explanation, researchers say, lies in a previously undescribed structure they call the "visceral pillar" — a detached section of gut tissue that acts like a tether as the embryo's body lengthens faster than its digestive tract can keep pace. Because the yolk sac sits to the left side of the embryo, that tether forces the growing body to buckle and twist toward the right.
It's like when you adjust the length of a strap and the longer, buckling side of the loop twists.
Dr. Tetsuto Miyashita, Canadian Museum of Nature
The finding matters beyond snake trivia, according to Phys.org's coverage of the paper: the coiling mechanism is what allows snake embryos to pack an extraordinarily long body — proportionally the longest of any vertebrate — into the confined space of an egg without simply running out of room. The research had an unusual origin: Miyashita began the project during COVID-19 lockdowns in 2020, when lab access was limited, by having students comb published literature and museum image archives for embryo photographs rather than run new experiments.
The team's next step is examining whether the same tethering mechanism shows up in other elongated, limbless animals, such as caecilians and legless lizards, to see whether right-handed coiling is a snake-specific quirk or a broader rule for how animals build unusually long, thin bodies inside an egg.
