How Do Spiders Shed Their Skin?

Have you ever wondered how spiders shed their skin and grow?

 

molt growth

Chronological comparison of tarantula exuvia (exoskeletons). Notice the increase in size.

Like other arthropods, spiders has a protective hard exoskeleton that they have to shed periodically throughout their lives as they grow. “Molting” is a term that is used to describe this process.

During the time that leads up to the molt, which is referred to as the “pre-molt” period, a new slightly larger inner exoskeleton develops and is folded up kind of like a soft crinkled up plastic bag under the existing exoskeleton.

This new soft exoskeleton is separated from the existing one by a thin layer called the “endocutilcle”.

 

During the pre-molt period the spider secretes fluid that contains digestive enzymes between the new inner and old outer exoskeletons.

This fluid digests the endocuticle that separates the two exoskeletons and this process is what actually leads to the color changes that are commonly seen during the pre-molt period, such as the darkening of the abdomen and the fading of colors.

tarantula on its back

Lasiodora parahybana lying on its back as it prepares to molt. Notice the web mat that it prepared for the molt.

Spider molt split carapace

Trapdoor Spider Molting Upright: just as it started to pull itself out through the split carapace.

Once the endocuticle is completely digested the spider is ready to complete the molt, and at this point it flips over onto its back, and use hydraulic pumping action of “hemolymph” or spider blood, to split its carapace or headpiece open.

It then will slowly pull itself out of the old exoskeleton through this opening.

 

Spiders typically molt on their backs; however, it is not uncommon to see spiders molt upright as well, as I show in some of my videos on my youtube channel.

Trapdoor Spider Molting Upright

Trapdoor Spider Molting Upright.

At this point the spider is completely defenseless. Its entire body, including its fangs, is very soft (notice how they are white in the picture)… so it is very important to leave them alone and to not touch them at any point during the molting process. If the spider were to be interrupted mid-molt, its exoskeleton could start to harden prematurely, and it could get partially stuck inside the old exoskeleton, which could be fatal.

 

 

rose hair tarantula molting

Chilean Rose Hair Tarantula Molting.

 

If it were to feel threatened and try to defend itself it could damage its soft fangs. Tarantula fangs are soft and white initially after molting, and as they harden they turn red and then ultimately black. Using fangs while they are still soft can cause them to become deformed and non-functional once they harden, leading to starvation and death.

Green Bottle Blue Tarantula Molt

Green Bottle Blue Tarantula lying on its back resting and stretching after a molt.

Freshly molted spiders are also prone to fatal bleeding, loss of limbs if they were to be dropped, fall, or suffer any kind of trauma or injury during the peri-molt time period.

In the days following the molt the spider, again uses hydraulic pumping action of hemolymph to expand the folded up soft new exoskeleton. This process is what results in a larger sized spider following a molt.

After the spider expands its exoskeleton and increases in size, the new exoskeleton starts to harden as cross linkages form between chitin and arthropodin, which are the two molecules that make up the exoskeleton. This process can take anywhere between 4-6 days for a smaller spider, but for larger spiders like large tarantulas it can take up 1, 2, or even 3 weeks for their exoskeletons to completely harden. Therefore it is very important to not touch or bother spiders during this post-molt period because they are still very fragile.

trapdoor spider mirror image

Trapdoor Spider Post Molt: White = actual spider. Red = old empty exoskeleton.

Spiders are pretty much like a freshly painted wall during this time…you really need to wait until they “dry” before you touch them, or offer them any kind of prey items. Typically spiders will not attack prey items until they have completely hardened; however, that is not to say that they will not attempt to defend themselves and/or bite something if they feel threatened.

A good way to check to see if a spider is ready to be fed following a molt is to do something called a “water droplet test”. To do this one takes a dropper of water, and drops a droplet of water near the spider or tarantula. If it shows any interest or attacks the water droplet it is likely ready to accept prey and can be safely fed.

red fangs

Macrophoto of Post-Molt Red Tarantula Fangs

Another test one can do is to look at the spider’s fangs and check their coloration. If they are black, and no longer white or red, then that indicates that the spider’s exoskeleton has completely hardened. However, this fang check requires the tarantula to be up on the side of the enclosure for the fangs to be observed, which is not always feasible with some specimens.

 

 

What to do if your tarantula gets stuck in the old exoskeleton during a molt?

I am by no means and expert on this subject, and I have luckily never had to manually assist any of my tarantulas during a molt, but what I can say is that it is very important to not prematurely intervene during a molt. Like I said earlier, the amount of time it takes for a spider to complete a molt varies greatly, and manual assistance should only be attempted as a last-ditch effort to save your tarantula spider if it is truly stuck.

macro of molt

Macrophotograph of a tarantula during a molt. You can see it pulling its legs out of the old exoskeleton.

Personally I would give my tarantula spider at least a full day to complete the molt on its own. Young spiders can take as little as 20 minutes to molt, whereas some of my older ones can take up to full day to complete the process. You have to remember that spiders are incredibly fragile during this time, and although ones intentions might be good in trying to help them during the molt, one could actually wind up killing them just by touching them prematurely…so try to be patient.