Why do snake embryos twist to the right even before they are born? Scientists have found the answer

An international team led by Canadian researchers has solved a long-standing mystery concerning the development of snakes: why their embryos almost always coil into a right-handed spiral during the first few weeks. It turns out that it is not down to muscle movements, but to how quickly the body of the developing snake grows compared to its gut.

Details

The study has been published in the journal *Current Biology*. The authors collected images of more than 900 embryos from 39 species of snakes and other legless squamates, and then compared the direction in which they coiled.

It turned out that in the first few weeks after the eggs were laid, the embryos coiled almost exclusively to the right — from head to tail. At this stage, their muscles were not yet sufficiently developed, so the reason must have been purely mechanical.

A key clue came from a CT scan. It revealed an unusual structure: the embryo’s intestine is temporarily separated from the body’s axis and runs through the centre of the spiral, whilst remaining connected to the yolk. Whilst the body is rapidly elongating, the gut ‘cannot keep up’ with this growth and effectively acts as a kind of tie. Because of this, the long body bends and twists.

The direction was also easily explained: the embryo’s yolk is situated on the left, so the growing body moves towards the opposite side and begins to coil to the right. Later, as hatching approaches, the muscles mature, the yolk shrinks, and some embryos change their position. As a result, among snakes that are almost ready to hatch, both right- and left-coiled individuals are found.

Why this is important

This research helps us understand how snakes, whilst still in the embryonic stage, develop their extraordinarily long bodies — the longest amongst vertebrates at birth. It is also a rare example of how a complex form arises from a relatively simple biomechanical process.

The authors believe that this model could also be useful for studying other spiral structures in nature – from intestines to shells. In other words, the mystery of snake embryos may help explain a more general principle underlying the formation of ‘coiled’ shapes in animals.

Source

Study: “How snake embryos coil”. Authors: Alexandra Weber et al. Journal: Current Biology, 2026. Further details can be found in the Canadian Museum of Nature’s press release. Published on 31 August 2026.