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How Strong Are Turtle Shells?

The shell is the turtle’s first and last line of defense, which they rely on to survive attacks from all manner of predators. Turtles may be slow and easy to catch — but they are tough to crack. Their strong shells mean that very few animals can successfully kill or seriously injure them. 

So how strong are turtle shells?

Amazingly, the shell is known to be stronger than concrete and even metals such as aluminum! Sufficed to say, the turtle’s shell is very strong, but it’s not invincible and animals such as dogs can still seriously injure the turtle.

In this article, we’ll tell you more about the shell’s resiliency, as well as what diseases and which animals may compromise the turtle’s formidable defense. Those shells are really quite fascinating, so stick with us and we’ll tell you all about them!

A Galapagos Giant Turtle has quite a formidable shell
A Galapagos Giant turtle has quite a formidable shell.

What Makes Turtle Shells So Strong?

Turtle shells are strong, no doubt about it, but what is it that makes their shells such a formidable defense? To answer that question, we need to look at its composition. In the simplest of terms, the shell is made of bones, keratin, and flesh.

The keratin and the bones in the shell are what give it its strength.

The shell consists of dermal plates underneath the skin, and that skin is covered in horny plates known as scutes. These scutes are made of keratin — the same material that makes up human nails and hair.

Keratin is also what makes up hooves, claws, horns, feathers, scales, and other epidermal appendages found in vertebrates. It is a strong and flexible material and makes for strong and tough appendages such as horns, claws, and of course the scutes of the turtle shell.

The shell can be divided into the carapace and plastron, with the carapace being the upper shell, while the plastron is the lower shell. The plastron also consists of the bridge which fuses the the carapace and plastron together.

The scutes of the plastron are just as tough as the carapace ones, but generally lighter in color. Let’s take a look at the carapace and plastron individually so that you may better understand how they combine in full defense of the turtle.

When you’re done here, you can also find out more about what’s INSIDE the turtle’s shell. Link opens in a new window so you’ll have it ready!

What Makes The Carapace So Strong?

The carapace is the convex upper part of the shell. Its foundation is the ossified ribs of the turtle, fused with dermal bone. ‘Dermal bone’ simply means that it is bone formed in the skin, rather than within the main skeleton. This is something that turtles have that humans and most other animals don’t.

These dermal bones form part of the shell and the turtle’s spine is also part of the carapace, fused to dermal plates formed underneath the skin. Atop the skin are scutes made of keratin, which makes them both hard and flexible and capable of withstanding a lot of pressure.

Some turtles have keels on their carapace, which refers to a ridge that goes down the back of the turtle.  Map turtles (Graptemys) are a good example and they have very visible keels on their shells.

While there are other animals that have hard shells and protective armor, the type of shell the turtle has is unique, as the carapace is essentially a fortified structure composed of transformed vertebrae and ribs!

What Makes The Plastron So Strong?

The plastron is the underside of the turtle and is commonly referred to as its belly. It is nearly flat, usually of a lighter color than the carapace, and it consists of both the flat ventral surface, as well as the bridge.

What makes the plastron so strong? Well, the plastron consists of nine bones and two epiplastra. which are bone structures found at the front edge of the plastron. This structure also has scutes, which make it stronger and also contribute to the structural integrity of the shell.

Close-up of an unidentified turtle's shell to show texture
Textured planes on a turtle’s shell also help to deflect damage.

How Tough Is A Turtle Shell?

So, how does science determine just how tough the shell is? One way to do so is to evaluate the fracture toughness of the shell. Fracture toughness, in simple terms, refers to how resistant a material is to cracking. The tougher a material is, the more force you’ll need to crack it.

The fracture toughness of a turtle shell is 36.4 MPa√m, which sounds pretty complicated, so we’ll give you some reference points. Glass generally has a fracture toughness of less than 1 MPa√m, while aluminum alloy has a fracture toughness of 14 to 28  MPa√m depending on the alloy composition.

Similarly, the fracture toughness of low-carbon steel is 12 MPa√m, and the average fracture toughness of steel is about 39.6 MPa√m.  High-carbon steel has a fracture toughness of about 92 MPa√m and Titanium alloy has a fracture toughness of 28 to 108 MPa√m depending on the alloy composition.

As you can see, a turtle shell is very tough– with comparative fracture toughness to steel, titanium alloy, and aluminum alloy!

Turtles also have impressive flexural strength, which is also known as bending strength, and this measures the ability of a material to resist deformation under applied bending stresses.

Simply put, it signifies how difficult it is to bend an object.

The maximum flexural strength of a turtle shell is 165.1 MPa. In comparison, concrete has a maximum flexural strength of 6.2 MPa. The maximum flexural strength of M20 concrete mix is about 4.8 MPa (after 28 days). M20 concrete mix has a ratio of 1 part cement, 1.5 parts sand, and 3 parts aggregate (stones).

With such impressive fracture toughness and flexural strength, it comes as no surprise that turtles can survive the bites and rough handling of many aggressive predators such as raccoons, possums, alligators, crocodiles, bears, and even wolves.

Even so, the turtle isn’t invulnerable, and their shells can still be broken. It is just VERY difficult to do so.

Not all turtles have hard shells. Some turtles, such as the leatherback and freshwater softshell turtles such as the Florida and the black softshell turtle lack hard rigid shells. Instead, they have flexible leathery shells.

Freshwater softshell turtles are known as trionychids and they are members of the taxonomic family Trionychidae. Some that are commonly kept as pets include the Chinese softshell (Pelodiscus sinensis) and spiny softshell (Apalone spinifera).

Turtles are quite slow compared to other animals out there and generally less aggressive than other animals, and these two characteristics make them easy targets. Thankfully, those tough shells offer superior protection and improve their chances of survival in the wild.

Of course, there are fast turtles and more aggressive turtles out there, but they are few and far between. For the most part, these are slow and peaceful creatures, so it’s a good thing that Nature stepped up and provided their formidable shells!

Curious how veterinarians fix a cracked turtle’s shell? We’ve got advice from a herpetologist that can tell you how it’s done!

A nesting sea turtle with a broken shell spotted in Costa Rica
Strong-jawed predators and diseases like shell rot can sometimes compromise even the toughest shells.

Diseases That Weaken The Shell

While a turtle shell can withstand thousands of pounds of pressure without cracking, certain diseases can severely compromise the shell and render it useless. Thankfully, very few diseases can do this, with two being most prominent for their adverse effects, and these are called ‘shell rot’ and ‘shell pyramiding’.

Shell Rot

Shell rot is also known as Septicemic cutaneous ulcerative disease (SCUD) and is a disease that affects turtles. The bacteria responsible for shell rot is called Citrobacter freundii and it sometimes works hand in hand with Serratia bacteria.

This is because the Serratia bacteria makes it easier for C. freundii to compromise and enter the turtle’s system.

The bacteria enter the turtle’s shell through injuries, such as cracks, bites, cuts, or abrasions. Once the turtle becomes infected with shell rot, ulcers and pittings occur along the shell’s surface. These are very dangerous, as they can extend into the dermal bone below the shell.

When left untreated, the disease progresses into a septicemic infection, which means that the disease becomes widespread throughout the turtle’s bloodstream. At this point, it causes the degradation of the liver and other organs within the turtle’s body.

Worse, at this stage, the disease is fatal and can cause the death of the turtle.

Symptoms

Once the turtle is infected with shell rots, pits develop on the outer layer (scutes) of the shell. A smelly discharge under the scutes usually accompanies this, and the shell and skin of the turtle may have small bleeding spots.  The turtle often becomes lethargic and refuses to eat.

Symptoms of Septicemic cutaneous ulcerative disease (SCUD) or shell rot include:

  • Pits on the shell
  • Scute discoloration
  • Loose scutes that may come off
  • Soft areas on the shell
  • Smelly discharge under the scutes
  • An unpleasant smell coming from the shell, produced by discharge under the scutes
  • Loss of appetite
  • Lethargy

Prevention

To prevent shell rot you need to stop the proliferation of the harmful bacteria that cause the disease. This is accomplished most easily by simply keeping the enclosure squeaky clean. In addition to keeping it clean, you should also, ensure the enclosure is free of objects and sharp edges that can harm the turtle.

Here are things to keep in mind if you wish to keep your turtle free of shell rot:

  • Keep the enclosure clean.
  • Change the water in the enclosure regularly.
  • Once a month, disinfect the enclosure with a bleach solution. Rinse the enclosure thoroughly with clean water after cleaning the enclosure to flush out the bleach solution.
  • With terrestrial turtles, apart from cleaning the enclosure, you should also change the substrate. With aquatic turtles, change the water within the tank regularly.
  • Spot clean the enclosure and remove fecal matter, urates, and uneaten food particles, as these can promote an increase in bacteria.
  • Remove objects and edges that can cut, scratch, or abrade the turtle and its shell.

Sometimes you need to clean your turtle’s shell – Find out why and how it’s done in our handy guide!

Treatment

Treatment involves cleaning the wounds and administering antibiotics to the turtle. A veterinarian may need to become involved in serious cases, so that they may keep the turtle at the clinic for monitoring if the disease is severe enough.

Usually, chlorhexidine solution is applied topically to the pits, wounds, and affected areas as an effective treatment measure.

A Nile crocodile becomes very aggressive when it feels threatened
Nile crocodiles routinely prey on Speke’s hinge-back Tortoises and East African black mud turtles.

Animals That Can Break The Turtle’s Shell

Although the turtle shell is incredibly strong, there are several animals out there that can break the turtle’s shell. These animals below are considered the turtle’s natural predators and while they aren’t always successful, the animals we’re listing have broken enough turtle shells to be considered a danger.

Honey Badger

Mellivora capensis, also known as ratel, is found throughout most of sub-Saharan Africa, the Arabian peninsula, and the Indian subcontinent. These animals can weigh up to 26 lb (12 kg) and they use their powerful jaws to crush the turtle’s shell.

The turtle is one of the favorite prey animals of the honey badger, as they have evolved powerful enough jaws capable of crushing the turtle’s shell.

Crocodilians

These include alligators, crocodiles, caimans, and gharials. Known for their powerful jaws and strong teeth, these creatures are quite capable of crushing a turtle’s shell – but only some of the time.

Due to the formidable nature of the turtle’s shell, crocodilians are not always successful in cracking it, and the turtles sometimes escape.

Dolphins, Sharks and Whales

Another set of animals that can break the shell of a turtle are several species of sharks, dolphins, and whales. Orcas (Orcinus orca), for instance, can break the shells of sea turtles with relative ease. These sea mammals have powerful jaws, sharp teeth, and enough bite force to get the job done.

Great white and tiger sharks can also break the shells of sea turtles quite easily, and turtles make up a substantial portion of their diets.

Birds

Many birds of prey, such as eagles, can break the shell of the turtle. While their beaks and talons aren’t powerful enough to break it, they can carry the turtle up into the air and drop it from great heights. The fall typically ends on rocky strata and this is sufficient to break the shell.

The golden eagle is one of the animals that uses this strategy to dine on unlucky chelonians.

Dogs

Dogs have powerful jaws and strong teeth, and large canines such as rottweilers can bite hard enough to break the shell of a turtle. As such, it is important to keep dogs and also cats away from turtles – both are capable of injuring or even killing a turtle.

If you’d like to learn more about how animals can break a turtle’s shell, Pets on Mom has a great article on the subject and you can read it here.

Video – Jaguar Trying To Eat Tortoise

Frequently Asked Questions

Do turtle shells break easily?

No, they do not break easily at all! Turtle shells are very strong and can withstand a lot of force, to the point that very few animals can break them. In fact, the turtle shell has a fracture toughness of 36.4 MPa√m and to put that into perspective, aluminum alloy has a fracture toughness of 14 to 28  MPa√m.

Needless to say, this toughness allows the turtle’s shell to withstand a very large amount of force.

Can a bullet break a turtle’s shell?

This depends on the caliber of the gun that fires the bullet and the distance between the gun and the turtle, but the answer is usually yes. Bullets fired from large-caliber guns can easily break the shell, but smaller-caliber guns won’t always be able to unless fired from a close distance.

Can a hammer break a turtle shell?

Yes, a hammer can break the shell of a turtle and we’ll tell you why. A hammer is a tool that is specially designed to create a focal point of force centered on a small metal surface, in order to transfer that force to a nail.

As such, when it is swung hard enough and continuously, a hammer puts all that force onto a small area of the shell the size of the hammerhead, and this application of force and metal can and will break a turtle’s shell.

How Strong Are Turtle Shells? The Conclusion

Turtles have very strong shells that can withstand high amounts of force and pressure. As the turtle’s main defense against predators in the wild, these strong shells do their job admirably, protecting the turtle from most predator attacks.

The shell is made of bone, skin, and keratin, and consists of dermal plates underneath the skin which are covered with horny plates known as scutes (composed of keratin). The dermal bone and the tough scutes work together to ensure that the shell is tough and can withstand whatever nature throws at the turtle.

To give you a proper perspective, it’s stronger than M20 concrete and has toughness comparable to aluminum alloys and steel. As far as evolutionary innovations go, a turtle’s shell truly is one of Nature’s most amazing marvels!

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