The term exoskeleton is originally a biological term, and is used to describe a type of skeleton in an animal. The word is made of two parts, ‘exo’ meaning outer, and ‘skeleton’ meaning the body part which forms the supporting structure of the organism. The meaning of the word is hence an external structure which supports the animal.
It was introduced to the English language by Sir Richard Owen (1804-1892), and in natural terms it was used to mean the external covering of an invertebrate animal for cover, support and protection. It can be seen in animals such as crustaceans and insects.
Humans, along with all mammals, have an endoskeleton, which means an internal support structure, or skeleton within.
Woodlice, Ants and Crabs are common examples of animals with exoskeletons, and exoskeleton animals can vary greatly across these species.
Animals that have exoskeletons differ from endoskeleton animals in many ways – the most obvious is size.
The proportional strength of a small muscle to a large muscle is not linear. For example, a muscle that is half as big has more than half the strength of the muscle that is twice as big. This is why an ant can lift vast weights in proportion to their body weight.
An ant’s muscles are on the inside of their skeleton, attaching to the inner wall of the exoskeleton.
An ant’s muscles are on the inside of their skeleton, attaching to the inner wall of the exoskeleton. It would be like human muscles all being contained inside the bone marrow section.
Mammals instead have layers of skin, veins and muscle above their skeletal structure. Every muscle is attached to a bone with many other muscles overlaying each other. Take your thigh for example, there are 4 major muscles near the surface of your thigh which allow for the motion of flexion/extension, adduction/abduction and rotation. This is why the area is called the quadriceps.
Having exoskeletons, insects can perform super biomechanical tasks, such as lifting 5 times their body weight or jumping incredible distances compared to body length. Often insects and crustaceans can live in environments too hazardous for mammals, and this can be due to the evolution of their exoskeleton.
Having exoskeletons, insects can perform super biomechanical tasks, such as lifting 5 times their body weight or jumping incredible distances compared to body length.
Crabs have very hard shells for protection, to withstand predatorial attack. Our endoskeletons do not offer us protection in this way.
There is a limiting factor to the size that a natural exoskeleton can grow too. We don't see any human sized insects and this is because the weight of an exoskeleton is much greater than an endoskeleton when compared at relative size.
Often made without calcium, exoskeleton structures are lightweight, but if grown to larger scales they would weigh too much for the muscle-mass strength ratio. The insects wouldn’t be able to lift their own limbs.
The exception to this rule is for animals that live in water. The difference in pressure underwater allows the exoskeleton to grow much larger. This is because the size of the muscles can lift the weight of a limb while in water. The Japanese spider grab is the largest known creature with an exoskeleton, growing to over 12 feet in span.
Another limiting size factor is that the animal must shed the external exoskeleton to form a new one, this often requires the replacement skeleton to be soft to allow it to escape the hard exoskeleton. The soft exoskeleton then solidifies. For a time, this makes the animal vulnerable to attack.
Despite the apparent dominance of endoskeletons in the larger forms of animals, it is estimated there are 200million insects, with exoskeletons, for every person on the planet. With an article in the New York Times claimed there are 300lb of insects for every 1lb of humans on the planet.
Exoskeletons are remarkable in the natural world and have advantages in many areas within nature.