November 11, 2026, 3:41 pm | Read time: 9 minutes
A seemingly dead spider that’s been hanging in the corner of the room or in a web for ages? A closer look reveals: It’s not a “real” animal anymore. Spiders must regularly shed their old skin to grow. What’s left behind is an empty shell that looks deceptively real. Biologist and editor Saskia Schneider, who kept spiders for years, explains how molting works, why it can be dangerous for the animals, and what owners of tarantulas and jumping spiders should know.
Molting is Part of a Spider’s Life
If you find a seemingly dead spider in a corner of the room, in the basement, or among plants, take a second look. Sometimes what appears to be a complete spider is actually just its old shell.
But this looks deceptively real, as even the legs, head, and sometimes the mouthparts are still visible. By this time, the actual spider has long since shed its old skin.
For spiders, this process is part of life: They must molt to grow. Molting is not easy for the spider and comes with some risks. Some spiders can spend hours freeing themselves from their old exoskeleton. If something goes wrong, a spider can even get stuck in its own skin.
Why Do Spiders Have to Molt?
Unlike humans, spiders do not have an internal skeleton made of bones but an exoskeleton. This hard shell, called the cuticle, consists of several layers and contains chitin and proteins. It protects the spider, gives its body stability, and helps prevent water loss.
However, this stable construction has a significant disadvantage: It doesn’t grow with the spider. As a young spider grows, it must shed its too-small armor and replace it with a larger one.
Also interesting: How old do spiders actually get?
Which Spiders Molt?
This happens frequently during youth. Many of the true spiders encountered in everyday life, the Araneomorphae, molt until they reach sexual maturity, according to Cornell University. It’s different for tarantulas and other representatives of the more primitive Mygalomorphae: Especially females can continue to molt as adults.1
Some time before the actual molt, a new exoskeleton begins to form under the old cuticle. Initially, it lies folded beneath. At the same time, the old shell increasingly detaches from the body. Then comes the most challenging part: The spider must emerge from itself.
How a Spider Emerges from Its Old Skin
Looking at a spider’s skin, it’s hard to imagine how the owner could have emerged from it. After all, it must pull not only its body but also both palps, its mouthparts, and eight long legs out of the old shell.
An unusual mechanism helps it do this. The spider shifts a large portion of its hemolymph, the body fluid of arachnids, from the abdomen to the front body. According to Cornell University, more than two-thirds of the hemolymph in the abdomen can be moved toward the front body. The increasing pressure eventually causes the old armor of the front body to open.2
First the Head – Then the Legs
Now the spider begins to work its way out of its old skin. Legs, palps, and mouthparts are gradually pulled out. Then the spider pumps fluid into its legs again, stretching the still-soft new exoskeleton to its final size.
This is fascinating because spiders partially move their legs hydraulically. Muscles can pull the legs inward, but for movement in the other direction, the pressure of the body fluid plays a crucial role.
The actual growth occurs mainly during the short time when the new exoskeleton is still soft and stretchable. Afterward, the cuticle hardens, and the body size is largely fixed until the next molt.
Why the Empty Spider Skin Looks So Real
What’s left behind is the so-called exuviae, and it can look remarkably similar to its former owner. After all, it’s not just a thin skin that’s shed. The spider leaves behind large parts of its old exoskeleton.
That’s why a well-preserved exuviae can still show eight legs, the front body, and other fine structures. If you find a seemingly dead spider, you can check if it might be a hollow, opened shell.
For tarantulas, the discarded skins even have an additional use for experienced keepers: A sufficiently well-preserved exuviae can often be used to determine the animal’s sex.
Also interesting: These spiders are suitable as pets
Dead Spider or Empty Shell? How to Tell
But how can you tell if the seemingly dead spider in the corner of the room is really deceased or just a shell? For most people, this question probably won’t arise. But for all spider enthusiasts, here’s the answer: Take a close look at the abdomen. The cuticle is usually softer and more elastic here. In many molts, this part shrivels, while in living spiders, it is very pronounced.
Another clue is the head. Often, the upper part detaches and stands up like a lid, allowing you to see inside the exuviae. Admittedly, for most native spiders, a magnifying glass is necessary to really see these details.
Why Molting Can Be Dangerous for Spiders
Molting is also one of the most vulnerable phases in a spider’s life. The new exoskeleton is initially soft and offers significantly less protection. At the same time, the animal can only move with difficulty. They are defenseless against predators.
Many spiders therefore retreat to a protected place before molting. According to Cornell University, true spiders often hang from a silk thread to molt, while tarantulas can create a substrate of spider silk.
When Spiders Get Stuck
The main problem is when the old shell cannot be completely shed. Unfavorable conditions, including humidity unsuitable for the species, can promote molting problems. If individual limbs get stuck in the old cuticle and the new exoskeleton begins to harden, legs can remain deformed. In the worst case, the spider does not survive the molt.
The reality of this danger is shown by a specimen in the Natural History Museum in Karlsruhe. There is a Goliath birdeater (Theraphosa blondi) nicknamed “Blondi,” which apparently got stuck at the front body and venomous claws during its molt. These hard, pointed structures can be problematic when being freed from the old shell.3
Lost a Leg? The Next Molt Provides a Replacement
However, molting has another remarkable side effect: It allows spiders to at least partially regenerate lost limbs.
If a still-growing spider loses a leg, for example, a new one can appear during a later molt. Initially, this is often smaller than the other legs. Over further molts, the size difference can gradually even out.
Also interesting: This spider looks like the famous Pokémon
A Tarantula on Its Back – Is It Dead?
For tarantula keepers, an impending molt can look quite dramatic. Many animals reduce their activity beforehand, retreat, and stop eating. In species with urticating hairs, a bald spot on the abdomen can also appear increasingly dark. Under the old cuticle, the new exoskeleton is already visible.4
A particularly clear, but for inexperienced keepers unsettling, image often follows immediately before the molt: The tarantula lies on its back.
What looks like a dying animal can be completely normal molting behavior. Some tarantulas even lay out a veritable carpet of spider silk beforehand. Then they assume their molting position and slowly work their way out of the old shell.5
Do Not Touch Spiders During Molting
National Geographic, for example, described the molting of a young Mexican redknee tarantula female, which took more than three hours. In the time-lapse video, the animal was seen lying on its side and slowly pulling its legs out of the old exoskeleton.6
For keepers, doing nothing is crucial in this situation. A tarantula in molting position should neither be turned over nor touched. Remaining feeder insects like crickets or locusts can be dangerous for a defenseless, freshly molted spider and should therefore be removed in time. Temperature and humidity should continue to meet the requirements of the respective species.
Even after a successful molt, patience is required. Not only the exoskeleton but also the fangs are initially soft. Only after hardening can the spider safely overpower prey again.
Jumping Spiders Also Need Peace for Molting
Not only the significantly larger tarantulas are increasingly kept as pets. Jumping spiders, for example, species of the genus Phidippus, now have many fans. And for them, too, molting is one of the most important and sensitive phases during growth.
In young jumping spiders, several molts follow one another, with the intervals potentially increasing with age. Before a molt, the animals often retreat into their web and may stop eating.7
Is There a Difference Between a Tarantula and a Bird Spider?
How Long Do Spiders Actually Live?
When Keepers Should Intervene and When Not
As unsettling as a molt can look, the spider usually manages it on its own. Especially with pet spiders, trying to help can do more harm than good.
Tarantulas should neither be taken out of their hiding place nor touched or pulled out of their old skin during molting. The keeping conditions should not be suddenly completely changed just because a molt is imminent. What matters are stable conditions suitable for the species and access to water.
If a spider actually gets partially stuck in the old skin, visibly loses body fluid, or shows severe misalignments after molting, that’s a different situation. For kept tarantulas, Jungle-Exotica.de recommends seeking expert help from a veterinarian experienced with reptiles or invertebrates, rather than pulling on the exuviae yourself.
An Empty Skin Tells a Whole Story
The next spider skin on the cellar wall or in the garden might be worth a closer look. What looks like the remains of a dead animal can actually mean the opposite: A spider has grown here.
For this, it practically rebuilt its body under the old shell, changed its fluid pressure, burst its armor, pulled eight legs out of thin shells, and then unfolded a new exoskeleton. And sometimes, during this process, a spider even regains a lost leg.