Spiders shed their skin, a natural and necessary process for their growth. Unlike humans and other animals whose internal skeletons grow with them, spiders possess a rigid outer covering. This external skeleton, an exoskeleton, provides protection and structural support. As a spider grows, its unyielding outer shell cannot expand, necessitating periodic shedding.
Why Spiders Molt and How It Happens
A spider’s body is encased in an exoskeleton, a hard, protective outer layer primarily composed of chitin and proteins. Since this non-living cuticle does not grow, spiders must undergo a process called molting, scientifically known as ecdysis, to increase in size and develop.
The molting process begins with a preparatory phase called apolysis. During this stage, the spider’s living tissue detaches from the inner surface of the old exoskeleton. Simultaneously, a new, soft cuticle begins to form underneath the existing one. Enzymes are released into the space between the old and new cuticles, helping to digest and reabsorb some material from the old shell.
Once the new exoskeleton is developed, the spider initiates shedding. This involves increasing its internal body pressure by pumping hemolymph into its cephalothorax. This pressure causes the old exoskeleton to split along predefined lines, such as the sides of the cephalothorax or around the abdomen. The spider then carefully extracts itself from the old casing, a process that can take several minutes to several hours, depending on the spider’s size.
The Shed Skin and What Comes Next
The discarded skin, formally known as the exuvia, is a remarkably accurate, though often translucent, replica of the spider. It includes the outer body covering and the linings of internal structures like the respiratory book lungs and the spinnerets, which are involved in silk production. Finding an exuvia indicates the presence of a growing spider nearby.
Immediately after molting, the spider’s new exoskeleton is soft and pliable, leaving it highly vulnerable. During this period, which can last from hours to several days, the spider is susceptible to predators and environmental threats. It seeks a secluded, protected location to recover and allow its new covering to harden.
The hardening process, called sclerotization, involves the cross-linking of proteins within the new cuticle, making it rigid and darkening its color. Once fully hardened, the spider regains full mobility and protective outer layer. Young spiders molt more frequently, sometimes every few weeks, while adult spiders may molt less often or cease molting entirely once they reach full size.