Spiders molt, a process known as ecdysis. This shedding of their outer covering is essential for their development. As arthropods, spiders possess an exoskeleton, a rigid external skeleton that supports and protects their bodies. This non-living structure does not grow with the spider, making periodic molting necessary.
The Molting Process Explained
The molting process begins internally as the spider prepares for a new, larger exoskeleton to form beneath the old one. Enzymes are released, which separate the old cuticle from the underlying epidermal cells. During this period, the spider may become less active and stop eating.
Once the new cuticle is formed, the spider finds a secure place to begin shedding. Many spiders hang upside down during this phase. The old exoskeleton splits, usually along the cephalothorax, the fused head and thorax region. The spider then extracts itself from the old shell, often by pumping hemolymph (their circulatory fluid) into its cephalothorax to increase pressure and split the old skin.
This process can take several minutes to several hours, depending on the spider’s size and species. The discarded exoskeleton, often called an exuvia, is a hollow, translucent replica of the spider, complete with leg casings and eye coverings. This exuvia indicates a molt has occurred.
Reasons Spiders Molt
Molting is primarily driven by the need for growth. Since the spider’s hard exoskeleton cannot expand, it must be periodically shed and replaced with a larger one. This process facilitates the spider’s development from a juvenile stage to an adult.
Beyond growth, molting also serves other biological purposes. It allows spiders to repair minor injuries sustained by the old exoskeleton, such as small cracks or punctures. Molting also provides an opportunity for the regeneration of lost limbs. If a spider loses a leg, a new, albeit sometimes smaller, limb can begin to grow back during subsequent molts, gradually returning to full size over several molting cycles.
Life After Molting
Immediately after molting, a spider is vulnerable because its new exoskeleton is soft and pliable. This soft state makes the spider susceptible to predators and physical damage. During this time, the spider remains relatively still, allowing its new cuticle to expand and begin to harden. The spider might absorb water or air to inflate its body and stretch the new, soft exoskeleton to a larger size before it hardens.
The hardening process, known as sclerotization, involves the cross-linking of proteins within the new cuticle. This process can take anywhere from several hours to several days, depending on the spider’s species and size. Only after the new exoskeleton has fully hardened does the spider resume its normal activities, such as hunting and web-building.
The frequency of molting varies throughout a spider’s life. Younger, rapidly growing spiders molt more frequently, sometimes every few weeks, as they need to increase in size quickly. As spiders mature and their growth rate slows, the molting frequency decreases. Most spiders cease molting once they reach sexual maturity and have attained their full adult size.