Spiders don’t have internal bones – instead, they have a strong exoskeleton made of chitin, which acts as a protective measure for spiders, that replaces bones.
Spiders belong to a group of invertebrates called arthropods.
One of the typical features of this group of animals that all the members share is the fact that they don’t have bones, nor do they have a spine.
Instead, spiders have survived for more than 100 million years thanks to their strong exoskeleton. This skeleton is made of chitin, and its main purpose is to protect the spider’s internal organs and against attacks from other animals.
Do Spiders Have Bones (Are they Vertebrates or Invertebrates?)
No, spiders don’t have bones. Their internal structure is supported by the external skeleton, which holds the body together and protects the internal organs.
Spiders belong to a group of animals called invertebrates.
The main feature of this group of animals is a lack of bones or spine. Some of these animals also have an exoskeleton, which protects the organs and holds the body of the animal together.
There are more than 140.000 animals in the group of invertebrates. It includes animals like spiders, but also insects, crustaceans like lobsters and crabs, mollusks, worms, and other animals.
But not all invertebrates have an exoskeleton.
Spiders belong to the group of invertebrates that do have an exoskeleton, while there are also other animals in this group that don’t have one. These animals include worms, squids, and other boneless animals that don’t have an external skeleton.
This exoskeleton has several functions that allow the spider to survive in the wild.
Read Also: Do Spiders have Tongues?
What Does an Exoskeleton Do?
Instead of bones, spiders have an exoskeleton which helps them survive attacks from other animals, protect their internal organs, and provide structure to their bodies as it allows them to move through harsh environments.
If you compare the structure of a spider to the structure of the human body, you’ll find that spiders don’t have bones, and their structure is completely different.
They’re invertebrates, meaning they don’t have a spine nor do they have bones.
To compensate for that, spiders have an exoskeleton which is made of chitin.
This skeleton holds all the internal organs together. If you take a look at the internal structure of a spider, you’ll find that most of the internal organs and tissues are not connected with bones, but they’re soft structures, which means the exoskeleton will have to do all the protecting.
These are some of the main roles that an exoskeleton plays for spiders.
- It protects the spider. By far the most important thing for spiders that an exoskeleton provides is protection. It enables them to repel attacks from other animals, because the exoskeleton is made of chitin, it is harder to break down. That’s why some animals won’t even bother to attack spiders.
- It protects internal organs. The internal structure of a spider is soft and vulnerable if exposed, which is why the external skeleton has to be strong enough to protect these organs.
- More strength. Compared to an endoskeleton (bones and spines), an exoskeleton gives more strength to the overall structure of the body. It allows the muscles to exert more strength, while the muscles in an endoskeleton are limited by the bone structure and the size of the bones. This means that spiders are several times stronger for their size.
Now, the exoskeleton will not grow together with the animal. To compensate for that, the spiders will have to molt their shell as they grow, which provides them with more space to grow.
Until they are fully grown, spiders will have to molt several times in their lifetime.
Read Also: Do Spiders have Antennae?
Do Spiders Have Spines?
Spiders are invertebrates, which means they don’t have spines or bones.
To replace the spine, spiders have an exoskeleton which holds the body together and bonds the internal muscles and structures.
Compared to animals that have spines, spiders aren’t able to stand up straight. Instead, they have more legs which are designed to hold the exoskeleton in place and move it around efficiently. To be more precise, spiders have eight legs that enable the skeleton to move as an entity.
This means that the structure of a spider’s body is not as complex as human body structure, for example, which has a spine.
For humans, the spine is the crucial element of the body that enables the body to move around in space, while spiders depend on their legs to do that, while the exoskeleton protects the internal organs.
So the fact that spiders don’t have a spine is not in any way detrimental to them. They have other benefits they gain with their skeleton, such as better protection against predators and better protection for internal organs, which are not exposed.
How Do Spiders Survive Without Bones?
Spiders have several adaptations that compensate for the lack of bones, such as the external shell made of chitin, and stronger legs that move the body around, as well as superior senses that allow them to sense vibrations.
This combination of features enables the spiders to survive comfortably in their habitats, even without bones.
But they have to live differently because of their lack of bones, so they can’t stand up straight. They have eight legs instead, which are powerful enough to hold the skeleton and move around swiftly.
They are also capable of creating intricate webs, which give them an advantage over other insects and animals they compete with for dominance.
Some spiders are also toxic, as they can bite the animal that is attacking and stun or disable it that way.
Spiders don’t have bones or spines, but they have a strong exoskeleton that will replace both. With this exoskeleton, they make sure they are protected from predators but also that they protect their internal organs.
The exoskeleton is made of chitin, which gives the external structure more integrity and protection against predators and adverse weather effects.