When a spider molts, it undergoes a biological process called ecdysis, involving shedding its rigid outer covering, the exoskeleton. This process is a necessary part of a spider’s life cycle, allowing it to grow and develop. Unlike the skin of many other animals, a spider’s exoskeleton cannot expand, requiring periodic replacement for growth.
The Purpose of Molting
Spiders molt because their hard exoskeleton restricts growth. As a spider grows, its existing exoskeleton becomes too small and inflexible. Shedding this layer allows the spider to emerge with a new, larger exoskeleton that expands before hardening. This growth is especially pronounced immediately after molting, while the new cuticle is still soft and pliable.
Beyond facilitating growth, molting also serves a regenerative function. Spiders can repair or regrow lost or damaged limbs with each successful molt. A spider might replace a lost leg, and while the regenerated limb may initially be smaller, it can regain its full size over subsequent molts.
The Molting Process Unveiled
The molting process begins with physiological changes initiated by hormones. These hormones trigger the production of enzymes that degrade the inner layers of the old exoskeleton, creating space between the old and new cuticle. During this pre-molt phase, the spider often becomes inactive, may stop eating, and seeks a safe, secluded location, sometimes spinning a silk mat for support. A new, soft exoskeleton, often folded to allow for expansion, develops underneath the old one.
Once prepared, the spider begins shedding, which can take minutes to days for larger species. The spider typically pumps hemolymph, its blood-like fluid, from its abdomen into its cephalothorax, causing the old exoskeleton to split, commonly along the top of the cephalothorax. The spider then pushes its body and appendages out of the old shell. Extracting all parts, including the lining of the lungs and fangs, requires significant effort.
Life After Molting
Immediately after molting, the spider is in a teneral state, characterized by a soft, pale, and flexible new exoskeleton. During this period, the spider is vulnerable to predators, desiccation, and injury, as its defenses are compromised. Many species remain hidden or inactive, sometimes hanging from a silk line or staying in a protective burrow, until their new covering hardens.
The hardening process, known as sclerotization, involves chemical changes that stiffen the new exoskeleton. This takes hours to days, or weeks for larger species like tarantulas. As the exoskeleton hardens, the spider may absorb excess fluid, causing the new shell to become duller. Until fully hardened, the spider cannot properly move, hunt, or defend itself.
Molting Frequency and What to Look For
The frequency of molting varies among species, influenced by age, growth rate, and environmental conditions. Younger spiders, rapidly growing, molt more frequently, sometimes every few weeks or months. As spiders mature, the molting frequency typically decreases, with some adult spiders molting only once or twice a year or less often.
Signs a spider is preparing to molt include refusal to eat, decreased activity, or abdomen darkening, particularly in tarantulas. After molting, the most obvious sign is the discarded exoskeleton, known as an exuvia. This cast-off skin is a hollow, often translucent replica of the spider, complete with leg casings, fangs, and eye coverings. Finding an exuvia indicates the spider has successfully completed this stage.