One of the intriguing things about tortoises is their ability to retract their heads and legs into their shells. Seeing a tortoise withdraw into its shield may make you wonder what caused it to happen.
Usually, tortoises hide in their shells to protect themselves from predators and harsh environmental conditions, including extreme heat or cold temperatures. Also, tortoises may retract their head when they’re introduced to a new/unfamiliar environment or due to illness.
Different species have different ways and reasons for retracting their heads. Sometimes, it could be a sign of illness. Below, we take a closer look at this intriguing phenomenon.
Why Does My Tortoise Hide in Its Shell?
Tortoises tend to withdraw into their shells when they:
Fear
Naturally, tortoises use their shells as safe shelters whenever confronted with danger.
According to the Herpetological Journal, tortoises have a powerful sense of smell and can smell predators as far as 26 feet away. This means they can pick up even the faintest smell and retreat into their shells out of fear, even if their predator is out of sight.
While pet tortoises meet few threats in their daily lives, they’re easily frightened by loud noises, such as the bang of a metal door. They are afraid of other pets, especially dogs, and can sometimes be spooked off by overly playful or loud children.
Depending on the tort’s personality, the voices of unfamiliar people may also trigger a full retraction.
Needs to Rest
Your tortoise may feel uncomfortable sleeping with its head and legs exposed. So, it may choose to remain under the protective cover of its shell.
Moreover, since tortoise shells don’t lose heat or warmth, they make a perfect cover against harsh weather. Remember, the more heat your tort conserves when sleeping, the more energy is conserved for other functions.
Catch Prey
According to Nature, tortoises originally developed their neck movement and retraction structures in the Jurassic period to catch prey. It wasn’t a protective measure as commonly thought.
Based on this study, it’s possible that modern tortoises inherited their neck retraction mechanisms from their Jurassic ancestors, who were mainly bottom-dwelling. They used retraction as a camouflage when hunting insects and other small animals.
Most tortoises are strictly herbivorous. However, omnivorous species, such as the yellow-footed and Asian tortoises, sometimes use ambush tactics to catch insects.
Since they’re not as fast as ordinary predators, these tortoises use their shells as cover. Here, they retract inside and hold still until the target bugs are close enough for a quick snap.
Of course, tortoises that do this don’t fully hide their heads, as they still need to keep track of their prey.
Distressed
If your tortoise is new to your home, there’s a chance that it could be distressed by the change of environment and the new faces.
Tortoises don’t dislike changes in their environment and tend to hide for the first few days as they try to come to terms with the changes. Don’t be surprised or worried when you notice your tortoise is hiding in its shell whenever it is outside the cage or in the presence of a new face.
Uncomfortable Temperatures
As mentioned, tortoises tend to hide under their shells to either conserve heat or to protect themselves from extreme heat. This may be from the sun or artificial heat sources.
This is often a temporary measure, and your tortoise will come out in an hour or so.
Tortoise Hiding in Shell All Day and Not Eating
As much as it’s normal for tortoises to hide in their shells, it’s unusual for healthy tortoises to hide the whole day and not come out to eat. While they don’t need to eat as much, healthy and active tortoises need regular boosts of energy and water.
If your tortoise stays hidden for days on end, it could be a sign of:
Brumation
Most tortoises brumate as a way to conserve energy during low temperatures.
This is unlikely to happen without your notice. Brumating is a natural phenomenon, and your tortoise may even benefit health-wise from a long rest.
Brumating tortoises remain asleep for most of the brumating period, although they’ll wake up to eat and drink once in a few days.
So, don’t worry much if you suspect your tortoise is brumating and doesn’t eat as much. Just ensure it gets all the food it needs when it eventually comes out to eat.
Illness
Tortoises have weak immune systems, and some illnesses can affect their mobility and energy levels. In most cases, sick tortoises prefer to hide in their shells whenever they’re out of their cages, as they have a heightened sense of vulnerability.
Dehydration
Tortoises need water for proper digestion, clear eyes, and healthy skin.
Your tortoise will become dehydrated if you don’t regularly soak your tortoise, give it clean drinking water, and feed it succulent foods.
Dehydration will not only endanger your tort’s health (by increasing the risk of kidney disease) but also affect its ability to move. Therefore, your tortoise may choose to stay hidden in its shell to conserve energy.
How Do Tortoises Hide In Their Shells?
A tortoise’s shell is fully connected to the body. Tortoise shells are hard and strong, often stronger than aluminum, and able to handle more than 100 times the animal’s weight.
The shells are made up of two fused sections; carapace and plastron. The carapace is the outer part and is essentially the vertebrae, consisting of more than 50 bones. Its outer layer is made of hard pieces of keratin, called scutes.
The plastron is the innermost part of the shell, and it contains the shoulder plates and part of the ribs. According to the National Academy of Sciences, the plastron is the most important part of the shell, as it defines the development structures of the vertebrate and that of the face and skull.
When it comes to the mechanics of retraction, tortoises can be broadly divided into two types: pleurodira and cryptodira. The different species falling within the two categories have different neck structures and, therefore, retract their heads differently.
Pleurodira
While this suborder mostly includes turtles, there are a few tortoise species, like the African mud terrapins, that fall within the category.
The name pleurodira itself translates to side neck and technically defines how these turtles bend their necks as they withdraw into their shells.
Pleurodires horizontally bend their heads and withdraw them to an open space beside one of the front legs.
This leaves some parts of the front legs exposed and parts of the neck. To make up for this and to further protect the tortoises from harm, most species have drooping carapaces covering most of the neck.
Cryptodires
The cryptodira suborder includes most tortoise species and marine turtles.
The name cryptodira translates to “hidden neck” in Greek and originates from how cryptodires completely hide their necks within their shells.
This is because they retract their heads on a vertical plane, first lowering their necks and pulling them back until they can fit in the space in front of their shells.
Neck Structure
Cryptodires have a wider cervical (neck) column, containing 9 joints and 8 vertebrae, all loosely connected.
The loose positioning, in particular, allows for more distension, which further allows the tortoises to bend their neck into an S shape during retraction.
While pleurodires have as many cervical vertebrae as cryptodires, theirs are more thinly arranged and have narrower cross-sections. Their horizontal or sideways neck retraction is made possible by the biconvex centra in some vertebrae.
These are double-joints and allow the neck to bend horizontally in both left and right directions. This is, as previously mentioned, the modus operandi of pleurodires.
Tortoises retract their limbs and neck into their shells whenever they’re scared or resting. There are times when they’ll also do it to rest or protect from excess heat.
Some species even do it as a way to catch prey. Hiding inside the shell should be a short-term endeavor and shouldn’t interfere with your tortoise’s ability to eat.
