If you have ever seen a group of turtles together you’ve probably seen them pile on each other. Why do they do this? The reason is actually quite simple.

Why Do Turtles Pile Up On Each Other?

Turtles pile on top of each other to get exposed to more sun-rays. They do this in order to receive as much UV as they can, and also for warmth. 

That’s the simple answer.

I have read on a few other forums and Q&A websites that some people thought that they did this in order to hide and protect themselves. Basically, that turtles aren’t fighting to get on top of each other. Rather, they are fighting to get underneath one another.

Logically this makes no sense, however. If this were the case, not only would we see them continually jockey for position, but the larger and stronger turtles would always be on the bottom. Instead, the larger and stronger turtles are sometimes on the top.

What’s happening when turtles do this is pretty basic.

Turtles need 2 things:

• UV rays from the sun
• Warmth to stimulate their metabolism and fight off infection

Very often in the wild there just aren’t many tall, open spots that turtles can get access to for basking. Instead, they need to make do with what they have.  This can be it a log, an open field, anything where they can get some rays.

The closer a turtle gets to the sun’s rays, the warmer it can get and the more UV rays it can soak up. Climbing on top of another turtle is a fairly easy way to accomplish this. 

Another Reason Why Turtles Stack On Top Of Each Other

There is another possible reason that I have read why turtles do this.  However, I have not found an academic source. That is is that turtles stack and pile on top of each other to make themselves appear larger than they are.

The reasoning is, in the wild when turtles are basking they often are quite vulnerable to predators. A lone turtle certainly is. But a group of turtles, all stacked and huddled together, makes them appear to be bigger and stronger as a group.

I’m not sure how valid this is, but it may be some sort of secondary evolutionary advantage to the stacking.

One turtle might stack on top of another when they are mating. There is also a study that showed turtles can be gay.

Does Turtle Stacking Hurt The Bottom Turtle?

In most cases, I don’t think you will have to worry too much about your habitat arrangement if you see your turtles stacking.

Potential concerns to turtle stacking would be things such as:

• This damaging weaker and smaller turtle’s shells.
• Less exposure to UV rays and warmth, possibly leading to disease or sickness.
• Bullying and fighting

I’ll quickly tackle these concerns one by one.

Absolutely not.

I actually found a really reasonable, well-thought-out answer to this question from a response on Quora. The author cited a paper published in the Journal of Mechanics of Materials and Structures, titled “Turtle Shell and Mammal Skull Resistance to Fracture Due to Predator Bites and Ground Impact” (talk about a mouthful!).

In the paper, the authors predicted that according to data, it would take a roughly 360-kilogram alligator to have enough bite force to pierce through the shell of a 2-kilogram turtle.

The Quora author, after doing a few calculations according to the bite force, found that if you were to extrapolate this data to turtle stacking, it would take about 240 1 kilogram turtles stacked on top of each other for the bottom turtle’s shell to be damaged. 

So rest easy. Even if you see 3 or 4 turtles stacked on each other, the turtle on the bottom is doing just fine.

Can Turtle Stacking Cause Sickness Or Disease From Lack Of UV? 

I really do not believe this to be the case.

In order for this to occur, there would have to be a number of variables at work:

• The bottom turtle should almost always be on the bottom.
• The turtle(s) on top should completely block all UV rays from reaching the bottom turtle.
• The turtle(s) on top should completely block all warmth from reaching the bottom turtle.

I have never experienced or read about all 3 of these factors working in congruence with another, and eventually leading to something like metabolic bone disease to the afflicted turtle.

For starters:

• Often 1 turtle will be on top one day, and the other on top another day, and so on, it’s not always the biggest and strongest turtle on top.
• The turtle(s) on top are often not blocking all or even most of the UV rays from hitting the bottom turtle.
• The turtle(s) on top is certainly not stealing away enough heat to make a significant difference in the heat that the bottom turtle is receiving

In order for a turtle’s health to be affected by this, there would just have to be too many things going wrong almost all the time, for a long period of time.

Can Turtle Stacking Lead To Bullying Or Fighting? 

Of all the possible reasons to be concerned about turtle stacking, this is probably the only one worth a bit of consideration.

That being said, I don’t believe turtle stacking is due to or leads to bullying or fighting in 99.9% of cases.

This would make sense given our original hypothesis, that turtles pile on top of each other in order to receive more UV rays and warmth, and also to make themselves appear larger to ward off would-be predators.

Moreover, at least in my personal experience, I have not noticed anyone turtle always on top. Very often it is one, but not always. If turtle stacking was an aggression or dominance thing, why would the smaller turtle sometimes be on top?

I just don’t think it adds up.

All this being said, what if you have more than 2 or 3 turtles, and you are concerned about this? What should you do?

How to Decrease Turtle Stacking in Your Habitat 

Let’s say that you are still unconvinced that turtle stacking isn’t problematic or harmful to your turtles, and that you want your turtles to stop doing this.

Luckily, the solution is usually quite simple.

As they are competing for the ideal basking spot, all you need to do is to increase its size. But not the size of the bulb. If you do that, you’ll have to manage the basking spot temperatures again, and the turtles would still pile up.

Instead, another option is to get two lower-watt basking bulbs and fixtures, and put them side-by-side or really close to each other. This does 2 things simultaneously:

• It increases the size of the basking area.
• It does not increase the size of the temperature.

This option tends to work better when you have 3 or more turtles in the same habitat. If you do, your tank or habitat should be sufficiently-sized as well, in order to accommodate not only all of the turtles but the larger basking space as well.

The other potential option would be to fix up two completely separate basking spots in your tank, but I wouldn’t recommend doing this.

• To begin with, it’s simply more of a hassle configuring everything this way.
• There’s a really good chance that your turtles will still huddle up together anyways.

Summary

• Turtles pile on top of each in order to receive more UV rays and warmth.
• This does not in way hurt the turtles on the bottom, nor does it lead to negative health consequences.
• If you want to decrease turtle stacking, consider using 2 lower-watt bulbs and fixtures side-by-side to increase the basking area without also increasing the temperature.