12 Things to Know About Spiders Molting


A molting spider may be an alarming or rather weird sight to a new spider owner with the constant shaking and falling onto its back. Most first-time spider owners might also not expect a creepy deposited exoskeleton, but there’s usually not much to worry about.

Spiders molt to develop a larger exoskeleton and facilitate growth. A molting spider may look like it is in distress or dying, but this is not the case. The process is relatively safe and entirely natural and should be embraced as part of your pet spider’s growth.

This article discusses the 12 most common questions about molting, including why it happens, how it works, and what you can do to make sure your spider molts safely.

molting tarantula

1. Why Do Spiders Molt?

Like humans, spiders have skeletons that help them move. However, unlike us, this skeleton isn’t found inside their body, but on the outside, like a suit of armor.

This armor is known as the exoskeleton and primarily consists of a strong but flexible fiber called chitin. Chitin and the structure of the exoskeleton allow a spider’s joints to move so it can walk and has extra flexibility for its stomach to expand after a meal.

Despite the adaptability of the exoskeleton, it cannot grow. While a spider certainly increases in size as it matures, its exoskeleton can’t expand with it.

This is where molting comes in. Molting involves a spider developing a bigger exoskeleton and shedding its old one to facilitate growth.

2. How Long Does a Spider Take to Molt?

Molting is a relatively complex bodily function and can take as little as 15 minutes to up to 24 hours. This varies from spider to spider, and there’s no real way of knowing beforehand how long your spider may take to lose its exoskeleton.

It’s also important to note that molting doesn’t end with the shedding of the old exoskeleton. The hardening of the new one can take anything between four days and three weeks. Usually, the bigger the spider, the longer it takes for its exoskeleton to harden.

3. How Often Do Spiders Molt?

Spiders usually stop molting once they reach their mature size. Most spiders will molt around eight times in their lives, although this number may vary according to the spider’s fully-grown size and the rate at which it grows.

Molting will occur more frequently while a spider is young. It can be as often as once a month in the first year of life.

Older spiders grow at a slower rate and will, therefore, only molt once every one or two years. Eventually, all spiders will stop molting entirely, though, indicating they have reached their full size.

4. How Does Molting Work?

Molting is divided into three loosely defined phases. Each phase involves a different stage of molting and takes varying amounts of time.

Pre-Molt

Before its old exoskeleton is shed, a spider develops the new one beneath it. During this process, the spider may become inactive. This is known as the pre-molt stage and can last for a few days to several months. The new exoskeleton is also made of chitin, although it is far softer than its older counterpart.

A layer of endocuticle separates the old and the new exoskeleton. During the pre-molt, the endocuticle is digested by enzymes secreted into this space through the spider’s hemolymph, or ‘blood.’

Molting

Once the endocuticle is completely digested and the nutrients produced are reabsorbed, the spider flips onto its back, and the shedding process begins.

Using hemolymph to pump up the pressure exerted on its rigid exoskeleton, it splits the old layer open. The spider then slowly extracts itself from the old exoskeleton and emerges with its soft, expandable new one.

Post-Molting

As soon as the spider extricates itself from its old exoskeleton, its body starts expanding to its larger size. The new, soft layer begins to harden as soon as it comes into contact with air. However, for the first few days after molting, the spider’s body will be soft and vulnerable to injury.

During the hardening process, spiders will move their legs a lot to ensure the new exoskeleton allows joint flexibility.

It can take weeks for the spider’s new exoskeleton to harden entirely, and only once this has occurred the process of molting is entirely complete.

Video of tarantula molting.

5. Does Molting Hurt a Spider?

Molting does not hurt a spider at all. Instead, it is a natural process necessary for the spider to grow and live healthily. Spiders are, however, more susceptible to injury and damage while molting. During this time, spiders are also far more sensitive to pain.

Although the molting process itself doesn’t hurt, outside factors may cause pain if the spider is not cared for and kept in the right environment.

6. Do All Spiders Molt?

Since molting is the only way any spider can grow, all spiders have to molt at some point in their lives.

molting large black tarantula

7. How Do I Know if My Spider is Molting?

Molting can be a worrisome occurrence for first-time spider owners. Recognizing the signs early on can put you at ease and reassure you your spider isn’t ill.

Signs that your pet spider is beginning to molt include:

  • Decreased appetite – Most spiders stop eating entirely once they enter pre-molt, although there are exceptions to the rule.
  • Large abdomen – Spiders who are about to molt often have expanded, shiny abdomens much larger than their standard size.
  • Their coloring darkens – This is primarily due to the digestion of the endocuticle.
  • Presence of a bald spot – Hairy spiders may often develop a bald spot on their abdomen once the molting process begins. The hairless area will disappear once the molting is completed.
  • Lethargy – Molting is a tricky process that takes up lots of energy. Spiders about to molt, therefore, usually reduce their movement and activity levels.
  • Lying on its back – This is the most common position for molting in spiders, although some spiders, like tarantulas, may suspend themselves in a web. If your spider is lying on its back, it is well into the molting process already.

8. Is My Spider Dead or Molting?

Many new spider owners may think their pet is sick or dying once the molting process begins. This is especially true once they see their spider lying motionless on its back.

A dead spider will very rarely be found on its back. When a spider dies, its legs usually curl up underneath it in its usual position. If your spider is lying on its back, it is probably molting, not dead. Do not touch it or disturb it during this time unless completely necessary.

If you’re not sure whether your spider is dead or molting, the best thing to do is to wait. If your spider is dead, touching it won’t change anything. However, if it is molting, touching it in the wrong way could be more harmful than helpful.

Give it a day or two and if there is still no change in its position, gently brush its legs with a paintbrush or something soft. If there is no reaction at all, there’s a good chance your spider has unfortunately died. Although not common, pet spiders can die mid-molt, which is why some dead spiders may be found on their backs.

9. Do Spiders Eat Their Molt?

If you’re wondering whether or not to remove your spider’s old exoskeleton from its enclosure or leave it there for them to snack on, you’re not alone.

There are mixed opinions as to whether or not spiders eat their molt, but the truth of the matter is it depends.

Some spiders may not be interested in eating their exoskeleton, while others may consume all or parts of it, especially the abdomen and book lungs.

Since the molting process is arduous and energy-consuming, your spider may be looking for something to eat as soon as it regains some mobility. If it chooses to eat its own molt, no harm can come from it, although it may look a little weird.

If you’re not sure about your spider’s molt-eating habits, leave the old exoskeleton in its enclosure for a day or two. If it hasn’t shown any interest in eating it, remove it.

10. How Can I Help My Spider When It Is Molting?

Molting is probably when a spider is at its most vulnerable to outside injury. After molting, its new exoskeleton is still extremely soft and can’t do much to protect it.

If your spider is molting, there are a few things you can do to aid the process:

  • Remove all prey from the enclosure – Even insects as small as baby crickets can injure a molting spider. Remove any other living creatures from your spider’s enclosure while it is molting to ensure no interference in the process.
  • Never touch a molting spider – For similar reasons as that for removing prey, it is vital you don’t touch or move your spider at all while it is molting. This could hurt it very severely and interrupt the process, causing various health risks.
  • Increase the humidity – Spiders rely on moisture to help them slip out of their old exoskeleton. If you notice your spider has begun to molt, look at increasing the humidity to ease the exhausting process.

11. What Are the Risks During Molting?

As mentioned above, the greatest risk to a molting spider is injury from prey insects in its enclosure or human interaction.

The other major risk to a spider during molting is getting stuck.

Getting Stuck in the Old Carapace

Sometimes this isn’t very serious, and the spider will extricate the body part that is stuck if given time. However, in other cases, a spider’s whole body may be stuck inside the exoskeleton, which is incredibly dangerous and could lead to death.

Difficulty removing itself from its carapace is usually due to low humidity. Lubrication is required if a spider is to remove itself from its hardened, old exoskeleton without being injured.

Around 85% of all pet spider deaths occur during the molting process. [Source]

The best way to prevent this from happening is to ensure your spider’s enclosure has high enough humidity to provide the moisture it needs for an easy molt.

12. What Should I Do if My Spider is Stuck in its Carapace?

Helping a spider stuck in its old exoskeleton is a delicate and tricky process. First, ensure your spider is really stuck by observing it carefully. If it isn’t moving or has removed part of its body but not all of it, there’s a good chance it needs a little assistance. This is the only exception to the “Don’t touch a molting spider,” rule.

Begin by increasing the humidity of its enclosure. If this does not seem to help, your best bet would be to wet a Q-tip or small, clean paintbrush and brush water gently across the carapace edge in the area it is stuck. The extra lubrication might help your spider complete its extraction by itself.

Continue this application of water for as long as it may take to help your pet get out of its exoskeleton.

If this still doesn’t seem to help, the last resort will be to gently pull on the old carapace with a popsicle stick and try to help your spider slide out. This is incredibly risky and shouldn’t be done if you have no experience dealing with a molting spider. If you’re unsure about this step, instead take your spider to an exotics vet who should be able to complete the process for you.

Conclusion

Molting is a complex, fascinating process to witness in a spider. Their ability to shed and regrow their exoskeletons makes them extraordinary creatures.

Although there’s not much we can do to help a molting spider, providing it with the right environment and enough time to go through this life-changing process will ensure your spider thrives and lives a long, happy life.

Brigitte Cave

Bridgitte grew up on a farm and eventually spent 5 years on Mahe Island in the Seychelles during her teen years. Her time living on a farm was spent mostly around animals including dogs, cats, cows, horses, and all sorts of fowl (chickens, ducks, and geese included). You can find out more about Bridgitte at https://mercurypets.com/our-writers/ Bridgitte is a keen horse rider and has competed in many showjumping competitions. She loves writing about pretty much all animals, and particularly dogs, cats, small mammals, horses and reptiles.

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