Tarantulas, like all species in the phylum Arthropoda, possess an exoskeleton, a rigid external skeleton. This external covering is a complex, multi-layered structure that serves as the animal’s primary support system and armor. This non-living, protective shell dictates much of the tarantula’s biology, including its physical form, movement, and necessary life cycle processes.
Structure and Function of the External Skeleton
The tarantula’s external skeleton, or cuticle, is a sophisticated biological composite material made primarily of chitin, a tough polysaccharide, cross-linked with various proteins. This chitin-protein matrix forms the bulk of the shell, providing both structural rigidity and flexibility. The skeleton acts as a structural framework, offering anchor points on its interior surface for muscle attachment, which allows for movement.
A thin, outermost layer called the epicuticle is composed of lipids and waxes. This waxy layer prevents the loss of internal moisture, a significant adaptation for arid conditions. The covering shields the tarantula’s soft internal organs from external threats and minor injuries. Hardness is achieved through sclerotization, where protein chains are chemically cross-linked, effectively “tanning” the shell.
The Necessity of Molting
Because the rigid exoskeleton cannot expand, periodic shedding is a biological necessity for growth. This process, known as molting, is also the only way the spider can repair significant damage, such as regenerating a lost leg. Preparation begins well before shedding, with the spider entering a pre-molt phase where it becomes lethargic and often refuses food.
During this stage, the tarantula secretes enzymes that dissolve and reabsorb the innermost layer of the old exoskeleton. A new, soft cuticle is simultaneously secreted underneath the old shell. When ready, the spider typically flips onto its back, allowing internal hydraulic pressure to assist the process. The tarantula forces its way out by rapidly increasing its blood pressure, causing the old cuticle to split along pre-determined lines. The entire process can take a few hours to a full day, depending on the spider’s age and size.
The Vulnerable State After Shedding
Immediately after emerging, the tarantula’s new external skeleton is soft, pliable, and often appears pale. This period is the most dangerous time in the spider’s life, as the lack of a hard shell leaves it susceptible to injury from predators or minor falls. The new skin is also inefficient at retaining moisture, increasing the risk of desiccation.
The tarantula must remain still and wait for the new exoskeleton to harden. During this time, the spider is immobile and defenseless, unable to hunt or properly defend itself. It typically takes several days for the new shell to become fully rigid. The fangs, which are part of the exoskeleton, must harden before the tarantula can safely resume feeding. It is recommended to wait five to seven days before offering food to ensure the fangs and body armor are fully functional.