Spurs are a unique part of a snake’s anatomy. Not all snakes have spurs, only ones that have remained unchanged for millions of years. The spurs on snakes are a ‘vestigial remnant.’
Spurs are tiny claw-like structures on either side of a snake’s cloaca. They are remnants of when snakes used to have legs, and are connected to small bones. They are used both for mating and fighting.
Some people mistakenly think that spurs are a build-up of unshed skin and nothing more. Although snakes no longer use their spurs for walking, they do still perform several valuable functions.
What Are Snake Spurs?
Cloacal spurs are a unique part of a snake’s anatomy. They sit on either side of the cloaca. They are like small spikes or claws poking out from under the snake’s scales.
The outside of the spur is solid like a horn or claw. It is usually a dark brown color. You can get your thumb underneath it and move it around, although your pet snake may not like it if you do.
But there’s more to a spur than meets the eye. The small claw-like appendage on the outside is only part of the structure of the spur. The rest is inside the snake’s body, and consists of a femur and a pelvis, which connects the two spurs together.
This pelvis isn’t connected to the snake’s spine. But they can still be moved around, to an extent, by the snake. If you have a pet snake with spurs, you’ll already know this. But what you might not know is why snakes have spurs.
Why Do Snakes Have Spurs?
A snake’s spurs can accurately be called a ‘vestigial remnant.’ This is a way of describing a part of an animal’s anatomy that has no clear current use. They are a remnant, a leftover, from a body part or organ that the animal used to need in its evolutionary history.
Snake spurs are a vestigial remnant of legs. Scientists can tell that they used to be legs because:
- The snake also has a remnant of a pelvis. This sits inside the snake’s body between the spurs
- Underneath the solid, claw-like exterior of the spur is bone which appears like a tiny femur
- The animal which snakes evolved from had short legs in the same location
Aside from that, taking a look at the spurs gives the same impression. If you were to dissect a snake, you could get a better look. You can see the bones the outer spurs are attached to, and they do look like femurs and a pelvis.
The question remains why snakes still have spurs, even if they can’t be used as legs. Most people would think that since the snake doesn’t need them, that evolution would have gotten rid of them.
The answer is that they’re still useful. Snakes with spurs still use them for several reasons.
How Do Snakes Use Spurs?
Despite not appearing very useful, snakes do still use their spurs. Males use them during mating in order to grip in place on the female’s back. They can also be used for fighting.
It’s these uses that mean the snake hasn’t gotten rid of its spurs completely.
Use of Snake Spurs During Mating
According to Copeia, the most crucial use of spurs is during mating. Mating is a complex ritual for snakes, involving many typical behaviors which are repeated across different snake species.
The male will find his way to a female. He will begin sniffing the air by rapidly flicking his tongue in her direction. If there are no other males around, he will approach her and start the next parts of the ‘ritual.’
He will next continue to approach her, getting closer and closer. When close enough, he will put his head on her body and slide on top of her. He will stop moving before he gets to her head. When his whole body is on top of hers, that’s when his use of spurs will occur.
At this point, the male will be writhing from side to side. He will also be moving his spurs quickly from side to side, almost like he’s trying to tickle the female.
After a while, he’ll start moving his spurs up and down rather than from side to side. He may do this quite hard. It encourages the female to lift her tail. He will then wrap his tail around hers for a cloacal kiss, which is where the pair finally mate.
Spurs are clearly a vital part of the mating process, at least for snakes that have them. But that’s not all they’re used for.
Use of Snake Spurs During Combat
Aside from the most obvious use during mating, spurs can also be used for fighting.
It’s mostly males that fight rather than females. Females don’t have as much need to fight, but males do. During the breeding season, many males will swarm towards a female that’s in heat. It’s then that they’ll fight, to ‘win’ the right to mate with her.
According to Herpetologica, certain species of boa use their spurs during these fights. The males will entwine their tails, as well as the lower halves of their bodies. They will keep their heads separated, probably to prevent any serious damage (because no mating rights are worth that).
They will then tug and pull at each other, trying to pin each other down. During this ‘fight,’ each male will use their spurs. They make their spurs stick out more than usual so that they can scratch or even puncture the enemy’s scales.
Whichever male is pinned, loses. The winner may get the chance to mate, unless another challenger decides to fight him.
This hasn’t been observed in every snake that has spurs. The research in Herpetologica only refers to the Madagascan boa. However, other species have likely figured out this use of spurs too.
So, if you notice your snake’s spurs sticking out, they’re looking for a fight or mate.
Male vs. Female Snake Spurs
It’s males that tend to have larger spurs. That’s because the longer their spurs, the easier it is for them to mate. And the longer their spurs, the more damage they can do to a competing male.
You might think that females don’t need spurs at all. But they do still have them even if they never use them. There are many analogous body parts in nature, like the appendix, or male nipples.
But even though they aren’t as useful for females, females do still have them. They are found in the same place as those of a male. The only differences are that they’re shorter and less curved.
Some people recommend that you can sex a snake by looking at their spurs. However, spur length, thickness, and curvature are all highly variable. One male could have long straight spurs, and another could have short hooked spurs.
A female could have long spurs, or slightly curved spurs too. Checking their spurs isn’t an accurate way to identify the sex of a snake. To check the snake’s sex, use popping or probing instead (or better yet, ask a vet).
Which Snakes Have Spurs?
Spurs are a remnant from earlier in the snake’s evolutionary history. It stands to reason that the more recently a snake evolved, the less likely it will have spurs. And, indeed, this is what you find.
Let’s take a look at some common pet snake species to see which ones have spurs.
Does a Boa Constrictor Have Spurs?
According to Science Daily, boas are an ancient species. They have remained unchanged for millions of years. Because they evolved relatively early in the history of snakes, they have a small pelvis unconnected to their spine as well as spurs.
Boids appeared in the Cretaceous period, around 70 million years ago. This was the point at which boas and pythons last shared a common ancestor.
The Cretaceous marked the first appearance of any snakes. Most of the fossils from the period show animals that are elongated like snakes, but they still have very short legs. It’s these creatures that boids generally, and then boa constrictors, evolved from.
The boa’s anatomy is unique in many ways. It’s possible to see how they evolved from a larger animal. They do have spurs, larger than most other snakes. But they also have two lungs, unlike most other species which only have one. One is much larger than the other.
Does a Ball Python Have Spurs?
Like boas, pythons evolved early relative to many other families of snakes. This means that they, too, have small spurs that used to be legs.
A ball python’s spurs are less obvious than those of a boa constrictor. A boa’s are thick as well as long. A ball python’s spurs are thinner and may appear more hook-like.
However, they are the same biological structure in both snakes. The difference is that those of a ball python has changed more over the years than those of a boa.
Does a Corn Snake Have Spurs?
Corn snakes don’t have spurs like boas and many python species. That’s because the snake family that corns belong to, the Colubrids, evolved later than boas and pythons did. In their evolution, they got rid of their spurs.
If you were to dissect a corn snake, you would find internal differences too. Corn snakes don’t have the pelvis or femurs that a python or a boa does. Over time, the corn snake got rid of these additional things as they had no need for them.