What is UV Light and Why is it Important for Box Turtles?


UV light is important for reptile health.

UV light is important for reptile health. Sunshine is one way for them to get it.
Modified version of photo by Chris Hsia @ Flickr; licensed under CC BY 2.0

Ultraviolet (UV) light is a part of the light spectrum (the whole range of light wavelengths) that is invisible to humans. The light we can see is in what we call the “visible spectrum.” We see these light wavelengths as colors. Animals see these wavelengths, too.

Some animals (including your box turtle) can also see parts of the UV spectrum, so they see more/different colors than we do. At least they do when they’re exposed to natural light (sunlight).

Some parts of the UV spectrum can also affect certain processes in your body.

There are three different kinds of UV rays: UVA, UVB and UVC. Some are good and can help your health (at least in moderation) and others are harmful. This is true for both humans and other animals.

So, what does this mean for your box turtle?

UVA Rays May Help Reptiles’ Mental Health

Many reptiles can see this kind of UV light. So it affects how they see the world. This means under natural lighting, they see the world very differently than we do. Under artificial lights without UVA, their world probably looks very similar to what we see. But again, very different from what they’re supposed to be seeing.

Does this matter? Do pet reptiles really need UVA to have a happy life in the little world we’ve created for them?

The answer doesn’t seem to be real clear. But evidence suggests that the presence or absence of these wavelengths affects how they act. They may be more active and more likely to interact with their environment if it looks normal to them.

This may in turn affect how happy and content they are. Some evidence also suggests they may have more normal appetites and breeding behaviors when they have UVA exposure than when they don’t.

Yes, we know reptiles don’t feel happiness or contentment the same way we understand those words. But they do have brains, and that means some level of mental process. The humane thing to do is give then an environment in which those mental processes function like they are supposed to. That means recreating as natural a habitat as possible. And that should include UVA light.

Luckily, the same UV lamps that supply UVB also supply UVA.

UVB Rays Help Your Pet Build Strong Bones and Shells

Which brings us to the question of just how important UVB rays are to your pet. To some degree, that depends on the kind of reptile you have. If you’re on this page, you probably have a box turtle!

Of course, many box turtle keepers also have other reptiles. And you may be wondering if you can treat them all the same. The answer? Not necessarily.

UVB and Vitamin D:

UVB rays are important to many animals (including humans) for making Vitamin D. Your skin makes a chemical called 7-dehydrocholesterol or 7DHC. UVB helps skin cells turn the 7DHC into Vitamin D (it’s actually a multi-step process, but that’s not important for this discussion). As far as we know, the process is the same or very similar in box turtles and other animals. Your pet’s body then uses the Vitamin D to process the calcium in his diet to build strong bones and shells.

What Happens Without UVB:

If your turtle does not get enough UVB, she can’t make enough Vitamin D. If she doesn’t get this important vitamin from other sources (hard to do), she’ll develop soft shells and bones. This condition is called metabolic bone disease (MBD). But even before it gets bad enough to soften your pet’s shell, it can cause her to be weak and lethargic. Egg-laying females and young turtles need more calcium than others. So they’re most at risk for MBD.

In young turtles, MBD can cause the shell to quickly become misshapen. The shell may grow unevenly or have odd lumps. In bad cases, the shell is so deformed that the turtle can’t close it. The hinge may even be frozen into one position. Although turtles can live after having had MBD, any deformities it caused will be permanent.

One quick note: As important as Vitamin D is, it’s not enough on its own. Your box turtle also needs to have enough calcium in her diet. If she doesn’t, her body will pull the calcium from her bones and all the Vitamin D in the world can’t change that.

The Problem with Vitamin D Supplements:

That said, it is possible to avoid MBD without using UVB lamps by feeding Vitamin D3 supplements. But the problem with this is that it’s hard to know how much to give. And too much can actually be deadly. When you provide UVB light, your boxie can regulate her own Vitamin D metabolism similar to the way she regulates her temperature—by moving in and out of the light.

This can make your life much easier, because you don’t have to know how much UVB or Vitamin D your pet needs. Which is good because even the experts don’t have a good answer to that question right now.

We do know that different reptiles seem to have very different UVB needs. And some studies of shed skin suggests that different reptiles’ skin lets different amounts of UVB through, too. Some reptiles, like bearded dragons seem to need a lot of UVB, spending much of the day basking. Others, like chameleons, spend much less time soaking up UVB and seem to make all the Vitamin D they need with those short exposures.

Box turtles seem to need less UVB than many reptiles, but they also love their basking time. In short, your pet knows better than you do what her UV and vitamin needs are. So leave it up to her.

UVC Rays are Dangerous

There is a third kind of UV ray, called (predictably) UVC. For the most part, the earth’s ozone layer filters these out of sunlight, and few if any reach us. This is a good thing, because they are harmful to you and your pet.

These are the rays that most promote diseases like skin cancer and eye damage. Too much UVA and UVB can also damage DNA and lead to skin cancer (UVB also causes burns), but UVC is the most dangerous. You may have seen UV disinfecting lamps used to kill germs. These lamps use UVC rays.

UVC is just as dangerous to your pet as it is for you and for germs. Make sure any UV lamps you use for your reptile’s habitat do not supply any of these rays. As long as you choose ones made especially for reptiles you should be safe.

Box turtle eating strawberryIf at all possible, it’s best to give your boxie time out in real sunlight. Even the best UV set-up can’t compete with sunlight. But when that’s not possible, a high-quality bulb that emits both UVA and UVB can help your box turtle feel more at home in his habitat and help keep him healthy.


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