Do Spiders Molt Their Skin?

Spiders (like reptiles, amphibians, and arthropods) shed their skin periodically throughout their lives in a process known as ‘molting.’ When they molt, spiders remove and discard their exoskeleton, the stiff, protective structure that encases their bodies. The new exoskeleton (which grows underneath) is larger than the one they cast off and has more room inside for them to grow.

But what is the purpose of molting, how often do spiders do it, and what happens to them during the molting process? Find out below!

What is molting?

Molting refers to the process in which spiders remove and discard their exoskeleton.

The external skeleton of spiders is different from the skin. It is a stiff, segmented support structure that surrounds the outside of the spider’s body, and is mostly made of chitin fibers.

This rigid (yet flexible) material supports and protects the spider’s body like a layer of armor, aiding movement and helping them to defend themselves against predators.

The segments of a spider’s exoskeleton are connected by joints, so spiders can move them back and forth with the help of muscles lining the inside of the structure and the pressure of internal bodily fluids. However, one thing this stiff exoskeleton cannot do is grow, which is why it must be shed at regular intervals.

Why do spiders molt?

Spiders must molt their exoskeletons in order to grow. This is because the exoskeleton is stiff and doesn’t expand as the body beneath it growths larger. Most species of spiders are minuscule when they first hatch; therefore, they will molt their exoskeleton several times over the course of their lifespan before they can reach their full adult size.

What happens when a spider molts?

The proper name for the shedding of the exoskeleton is ecdysis, and it is a highly complicated process. Spiders don’t simply wriggle out of their skin when they want to shed their exoskeleton; instead, they must go through a multi-step process that begins with the release of certain hormones.


Stages of molting

The process of molting is initiated by the release of ecdysis triggering hormones (ETH). When it is time for the spider to shed its skin, these hormones kickstart a sequence of processes by which the old exoskeleton is discarded and replaced with a new one.

Molting in spiders takes part in three stages. These are pre-molt, molt and post-molt.


During the ‘pre-molting’ stage, the spider begins to secrete a new, soft exoskeleton beneath the existing one. This new exoskeleton stays folded up beneath the hard, outer exoskeleton until the spider is ready to use it.

This new exoskeleton is larger than the previous one and is separated from the existing exoskeleton by a thin layer known as the endocuticle.

The endocuticle is broken down by enzymes, which are released during the ‘pre-molt’ stage. The nutrients from the endocuticle are reabsorbed and recycled by the spider’s body, which helps to compensate for the amount of energy required to grow the new exoskeleton.

The hard, outer exoskeleton remains in place throughout this process to protect the spider.


Once the new exoskeleton is formed and the cuticle separating it from the existing exoskeleton is completely broken down, the spider enters the molting stage (ecdysis).

During this stage, the spider must expand its body in order to break out of the old exoskeleton. It does this by taking in water or air (depending on its surrounding habitat), or by using the concentrated pressure of its hemolymph (spider blood).

This causes the outer exoskeleton to crack, and the spider wriggles free.


Immediately after ecdysis is complete, the spider’s new exoskeleton is very soft. During this stage, it is very vulnerable to attack by predators. The spider takes in yet more air (or water) to puff and enlarge the new exoskeleton even more, creating extra room for it to grow. Finally, the new exoskeleton hardens.

How often do spiders molt?

Molting happens most frequently when a spider is young and it is growing quickly, but some spider species continue to molt and grow larger throughout their lives.


Some spiders molt according to an internal clock’ and molt periodically after a certain number of days have passed. Other species may molt depending on the number of insects they eat.

The more bugs a spider swallows, the quicker it will grow and the sooner it will need to shed its restrictive outer exoskeleton.

Do all spiders molt?

Yes, all spiders molt their skin! This process is essential for allowing the spider to grow bigger and is a vital part of their lifelong development.

What other types of animals shed their skin?

It’s not only arachnids that shed their skin. The following creatures all molt their skin or exoskeleton to facilitate growth:

  • Reptiles for example snakes and lizards.
  • Arthropods for example crabs, lobsters, and scorpions.
  • Amphibians for example salamanders and frogs.


Molting, the process of shedding the exoskeleton to allow room for growth, is something all spiders do. This is a vital part of their development, as the exoskeleton does not grow as the rest of the body does. Therefore, it must be removed to allow the spider to grow larger.

Molting (aka ecdysis) is a complex and energy-demanding process that is triggered by the release of certain hormones. These initiate the secretion of a new, soft exoskeleton and the breaking down of the cuticle that separates it from the existing one. Once the new exoskeleton is completely formed, the spider puffs up its body using air or water to crack the old exoskeleton and wriggle out to freedom.

The new exoskeleton is very soft, leaving the spider vulnerable to predators and other spiders. Once it hardens, however, the spider is ready to resume life as an insect-slaying assassin, bigger and more fearsome than ever before.

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