- Snakes contract and release their body muscles up and down the lengths of their long body. What happens is, it creates a force at multiple points at the same time which activates the dorsal muscles.
- Snakes also use the act of straining muscles in that way costs significantly higher energy than other methods of movement.
- Zoologists have long identified four types of movement that snakes use to navigate their environments.
The strong limbs and remarkable metabolism of cheetahs allow them to reach land speeds of 80 miles per hour, while the common swift has developed a body and wings that allow it to stay in the air for 10 months at a time.
By contrast, the slither of the snake can seem a bit underwhelming.
These reptiles lost their legs through natural selection and have grown to cover every continent other than Antarctica without feeling any apparent need to go back.
But the over 3,000 distinct species of snake on the planet are a diverse lot. In many instances, we can see how snakes might have developed unique characteristics to help ameliorate the disadvantage of limited mobility when compared to nimble — and typically mammalian — prey like rats and rabbits.
Venom and camouflage are particularly common, but there’s more evolutionary sophistication at work here than the layperson might know.
Yet like all other reptiles, movement remains an important part of snakes’ ability to survive. So how do snakes move? Zoologists have long since identified four types of movement that snakes use to navigate their environments, but we’re continuing to learn more about the way snakes move.
We’re also discovering that there’s often significantly more nuance and the distinction between the movement style of snake species that might look identical to us.
Additionally, snakes are known for their S-shaped movements. However, they have a lesser-known skill – the ability to crawl in a straight line. Biologists believe the reason for this is to help them escape from confined spaces. Many heavy-bodied snakes such as vipers, boas, and pythons rely on this rather handy ability.
Researchers often propose new and more nuanced frameworks for explaining snake locomotion. Many of them are sensible options, but the four recognized methods continue to be the best-generalized framework that we have. Here’s what we know about how snakes move without legs.
1. Lateral Undulation
How do snakes move, frequently? What is one of their preferred methods for slithering from one point to another?
If you’ve ever seen a snake in the wild, chances are that it employed lateral undulation. It’s the most common form of movement for snakes, largely because it continues to be a very effective method of movement. The African black mamba is recognized as one of the world’s largest snakes, and they can achieve top speeds of 12 miles per hour with their traditional slither.
What appears to be a seamless and smooth serpentine motion across the surface of the ground is the result of the snake contracting and releasing muscles up and down the length of its body. By creating force at multiple points simultaneously and sequentially activating the powerful dorsal muscles down the length of their long body, they can effectively undulate their body forward in segments.
These muscles create momentum, but the head and neck are directing the body of the snake.
Lateral undulation has also propagated so widely because it’s such a flexible way to move without legs. The traction from their scales has transformed many snake species — including the green tree snake — into prodigious climbers.
Sea snakes laterally undulate to hunt fish in water, and they’ve even evolved fins that resemble oars to help them cross greater distances in water more effectively. Despite this, it’s taken some very specific modifications for snakes to be capable of moving in such a manner.
From the impressively flexible relationship between their spine and their skin to their scales designed to grip surfaces like a tire’s treads, the serpent’s trademark slither requires a convergence of highly specialized traits developing over an extensive period. But most impressive may be their fine motor skills, which have to be able to adjust to friction changes quickly and control the swing of the varying segments of their slithering body around obstacles.
Lateral undulation is the standard for most snakes, but it also appears to be one of the most complex. Researchers have noticed distinct differences in the patterns and behavior of undulating snakes, with particularly notable differences between snakes who undulate on land and in water.
As research develops, it’s likely that lateral undulation will eventually be categorized into a broader range of movement styles.
2. Concertina Locomotion
The method of movement known as concertina seems like one of the most straightforward approaches for movement. However, there’s a reason we see far fewer snakes rely on it compared to lateral undulation. To use this second method, snakes will arch their long bodies upward by straining the muscles, then use the extra length to push the front halves of their body forward and pull the back half behind.
It’s a straightforward form of movement that allows snakes to move in a straight line rather than requiring them to undulate, but the act of straining muscles in this manner results in significantly higher energy expenditure compared to other methods of movement. The fact that it is not ideal for speed is also another drawback.
A 2018 study focused on the fossils of reptile and snake skulls offers both a plausible premise for the long unanswered question of how snakes evolved from reptiles and a clue to why snakes would develop such a particular form of mobility. The newly believed ancestor of the snake appears to be a type of burrowing reptile, and natural selection eventually shrunk down the size of their legs to nothing.
This unique flexing approach would make sense for offering the forward momentum necessary to burrow through packed dirt and soil. While snakes that use the concertina movement may be thought of as being more primitive than other species, the truth is that this movement style is merely best specialized towards particular species in particular environments.
Most snakes that travel in this way come from large species like pythons and boas, but there’s also a preference for the movement style among arboreal species. The bridging motion of concertina movements makes it much easier to cross the distance between branches or limbs when traversing arboreal heights.
Sidewinder rattlesnakes are the serpents most famous for their sidewinding movement style, but they aren’t the only snakes to exhibit this behavior. Though functionally similar to the way that lateral undulation works, sidewinding snakes will let only a portion of their body touch the surface of the ground and use this as a focal point for adjusting the rest of the body.
This is more complicated than it seems, as a sidewinding snake lifts its body off of the ground. It may look like a chaotic and ineffective method of travel, but a sidewinder rattlesnake can reach speeds of up to 18 miles per hour in their habitats throughout Mexico and the American southwest.
Sidewinding seems to have very limited use throughout the larger snake community, but that’s just because it developed for the conditions of very specific habitats.
In the case of the rattlesnake and the Saharan horned viper, the challenge sidewinding arose to overcome is the loose and hot sand of the scorching desert. Minimizing direct contact with the sand and regularly shifting contact points makes it easier for a snake to avoid sand shifting underneath them.
Homalopsine is the exception. Found throughout Indonesia and Australia, these snakes use the sidewinding method of locomotion to navigate their muddy ecosystems. Desert sidewinders can cover great distances efficiently without legs, but they’re especially adept at climbing. By placing their weight as flush as they can to the dunes they’re climbing, they can ascend practically the steepest sandy surface.
4. Rectilinear Locomotion
How do snakes move when they need to make as little noise as possible?
Rectilinear locomotion is similar to concertina movement in that it allows snakes to walk in a straight line and tends to be a preferred form of navigation for larger snakes, but snakes make use of strong muscles along the abdomen rather than lifting themselves into high coils.
While this makes rectilinear locomotion a poor method for climbing trees, it’s believed to be rooted in the same method of burrowing that defined the locomotion of the earliest descendants of snakes. By lifting the body and pushing forward in slower and less dramatic movements, larger snakes can move at a steady clip while minimizing their energy expenditure.
Rectilinear movement is often a preferred choice in the largest snake species. That’s because while rectilinear movement is one of the slowest forms of locomotion, it lends snakes the ability to move nearly silently. That’s a distinct advantage for ambush hunters like boa constrictors. But for most snakes, rectilinear movement typically exists as a single tool in their larger movement toolkit.
Arboreal snakes, combine rectilinear movement with concertina locomotion when navigating through trees, and there’s some evidence that most snake species will employ it even when they primarily navigate using lateral undulation.
Rectilinear movement is also a preferred choice when a snake needs to squeeze through tight spaces or navigate tunnels. It’s proven to be such an effective method through difficult terrain such as mud and rocks that engineers have begun pursuing rectilinear motion as an alternative to wheeled robots.
Particularly in difficult environments, these types of robots show a lot of promise not just for environmental navigation but also due to their reliability and comparatively low rates of mechanical failure.
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