Why Do Turtles Stack? (with Pictures and Videos)

I’ve seen countless photos of turtles stacking one on top of each other, and I think that you’ve also seen a lot of similar pictures too. In the beginning, I thought that people just stalked them on top of each other for the fun of it. But by looking closer at those pictures this idea seemed less and less plausible. So I decided to do some research on why turtles stack, here is what I found out.

Turtles stack on top of each other to get exposed to more sun rays, which provide UV rays, which are essential for turtles. Some other common reasons why turtles stack are to generate heat and to defend from predators

Stacking is a normal thing for turtles. But this doesn’t make it any less fascinating. So let’s take a closer look at turtle stacks and see how they work, which turtle is positioned better, and what it means if your pet turtles are stacking.

How the Stack Works

Turtle stacks are very simplistic at first sight, but they are actually a bit more complex than that. By stacking, turtles manage to accomplish a lot of different things.

When multiple turtles are on top of each other they will generate more heat than they would have on their own. So every turtle in the stack, from top to bottom, will get this benefit.

The turtle at the top will also get a lot more UV rays than it would have on its own. While it’s true that not all turtles in the stack get this benefit at the same time., turtles will also change positions over time so that each one of them will get its fair share.

Turtle stacks also work as a defensive formation. Most smaller predators don’t consider a single turtle a problem so they will attack without hesitation, but for some of them, a stack of turtles will be a problem, so they will not attack them.

The process of forming a stack is quite simple. When turtles feel that they don’t get enough UV light, or that it’s getting too cold for them they will instinctively gather up in spots with direct sunlight and simply get on top of each other. 

Each position in the stack has its own advantage so turtles won’t fight too much over positions when they get on top of each other.

Which Turtle Is Positioned Better?

Overall all positions in the stack are beneficial, but we can’t say that all of them are just as good.

The turtle on top of the stack will get the most of the UV rays from the sun but it will also get some heat from the turtle below it.

The turtle that is at the bottom of the stack will get some heat, but not the most heat of them all because there is no turtle underneath. So from a heat perspective or a UV perspective, this is not the best position, but it’s still better than basking alone.

All turtles gain benefits from stacking, all turtles in the stack will get a lot more heat than they would have on their own, and the closer they are to the top, the closer they are to the sun, which provides them with UV rays, even if they don’t get the full benefits of them, since another turtle is partially covering them.

So will you see turtles competing for the top position that gets most of the UV rays? Probably no. While the top position can be considered the best most turtles seem not to bother too much to get on top.

Will you see turtles trying to avoid being the turtle at the bottom? Again probably no, even if it’s not the most advantageous position it’s still better than basking on their own. And at some point, they will get the chance to be in a better position.

Those positions are not permanent, even if most pictures online show stacks where the biggest turtle is at the base and the smallest ones are at the top this is not always the case. It’s not uncommon to see big-sized turtles on top of smaller turtles. So even the biggest turtle can have days when it’s going to be at the top of the stack.

Is Turtle Stacking Dangerous for the Turtles?

It might seem dangerous for smaller turtles to sustain bigger turtles on top of them, but there is no reason to worry. Turtle shells are very tough and a small turtle will have no problem sustaining turtles that are bigger and weigh 10, 15, or even more times their weight. But in most cases you won’t see the smaller turtle holding too many turtles on top of it just because it’s not practical, at some point the turtle on top will lose its balance if the turtle beneath is too small, or too many other turtles come on top.

The only reason why a turtle’s shell might get damaged from stacking is that the turtle was already suffering from shell rot, or it was severely damaged by a predator. Otherwise, the turtles are in no danger while stacking.

Why Are My Pet Turtles Stacking and What Should I Do?

The only reason pet turtles are stacking is because you have a bad basking area.

Your basking area could be too small in which case your turtles will be forced to stack on top of each other. This can be really bad because at some point your turtles will start competing for the top spot to get UV rays and one of them will end up dominating the other. The turtle that will be at the bottom will get far too few UV rays if that is the only position it can get.

Even if your turtles are evenly matched they can still hurt one another and this is again a problem. To solve this you should make sure that all your turtles have enough space to bask peacefully without having to compete for a better spot with the other turtles.

Your basking area might not be well heated. If this is the case your turtles will resort to stacking to get the necessary heat. To solve this you should make sure that the temperature is right for them. If this is your problem you should read my Guide for Lighting and Heating a Turtle Tank and Basking Area, in this guide, I cover everything that you need to know about the heating and lighting of the basking area.

Other Possible Reasons Why Turtles Stack

It is also believed that turtles do this to better protect themselves from predators. This seems logical, a predator won’t be as inclined to attack 5 or 6 turtles as it would be to attack just one. And they can seem a lot more intimidating from a distance even if the predator doesn’t know how many turtles are there.

As I said this seems logical but at the moment there is no concrete proof of this. Because turtles are really slow (but not as slow as you might expect) you won’t see them get into a stack as soon as a predator arrives. Another thing to contradict this theory is the fact that turtles spend most of their time alone so they wouldn’t normally develop “defensive maneuvers” that require teamwork.

So at the moment, this is just a theory that seems to be true, but there is no scientific proof.

Is Stacking a Social Activity?

It might seem at first like a social activity but it definitely isn’t. Turtles only do this because they need to and they are not interacting any more than they need to during this activity.

Turtles are very non-social animals and they like it that way, they are only social when they have to and that is during the mating season. Of course, there are a few exceptions to this, if you want to know more about the social lives of turtles and how they form colonies you should read this article: Are Turtles Social Animals?

Final Thoughts

Stacking might seem unnatural at first but after you find out the reasons it seems like quite a normal way to solve a problem.

At the moment we know that turtles stack to make up for the lack of good basking spots, but there are more theories out there, like the one about stacking is a way to defend from predators, but most of these theories are just that, theories. Most of them have no solid research to back them up. So at the moment, the only scientific reason for turtles to stack is to get better access to UV rays and heat.

If you have any questions about turtles that are turtle stacks or anything about turtles, feel free to leave your questions in the comment section and I will answer them as soon as possible.

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