Jumping spiders (family Salticidae) are recognized by their acute vision and characteristic hunting style. Like all arthropods, these spiders possess a rigid outer skeleton that prevents continuous growth. This necessitates a cyclical process of renewal known as molting (ecdysis). Molting involves shedding the entire external cuticle to accommodate an increase in body size, marking the transition between developmental stages.
Why Jumping Spiders Must Molt
The primary reason for molting is physical growth, since the spider’s hard exoskeleton cannot expand. The protective outer casing functions like armor, but as the spider grows, the exoskeleton becomes a restrictive shell that must be shed and replaced. The process begins with the secretion of a new, soft cuticle beneath the old one. This is followed by the separation of the old skeleton from the underlying epidermis (apolysis), preparing the spider to push out of its old skin (the exuviae).
Molting also serves a restorative function. The shed allows the spider to repair minor damage and replace lost or injured limbs. Although a regenerated limb may be smaller immediately following the molt, subsequent molts restore it closer to its original size and function. Replacing the outer cuticle also helps maintain the integrity of the spider’s body, as the exoskeleton can become worn over time.
Frequency Based on Life Stage
The frequency of molting changes dramatically throughout the jumping spider’s lifespan, correlating directly with its growth rate. The stages between molts are called instars, and a spider progresses through a sequence of instars before reaching maturity. Most jumping spider species, such as the Regal jumping spider, undergo approximately six to nine molts before becoming adults.
Spiderlings and juveniles experience the highest frequency of molting because they are growing rapidly. They may molt as often as every few weeks, especially when food is abundant and temperatures are favorable. The first molt often occurs while the spiderling is still inside the egg sac.
As the spider progresses through its juvenile and sub-adult stages, the time between molts increases. Early instars might be separated by three to four weeks, but later sub-adult molts have longer gaps. Once a jumping spider reaches sexual maturity, it is considered a full adult, and molting stops completely. The spider’s growth is finished, and the exoskeleton is finalized to support its adult form.
Navigating the Molting Process
The molting process begins long before the actual shedding of the old skin. During the pre-molt phase, the spider becomes lethargic and stops eating, often retreating to a secure location. The spider spins a dense silk retreat, known as a molting hammock or sac, which provides a protected, humid environment for the vulnerable shedding event. This preparatory stage can last for several days or a few weeks, depending on the spider’s age and health.
The physical act of shedding the exoskeleton, the ecdysis phase, is relatively quick but strenuous. The old cuticle splits, often along the cephalothorax, and the spider slowly pushes its body and limbs out of the old casing. This process can take just minutes for a young spider, though it may take several hours for older, larger individuals.
Following the shed, the spider enters the post-molt phase, during which it is highly vulnerable. The new exoskeleton is soft and pliable, making the spider defenseless against predators and prone to dehydration. The spider remains inside its silk retreat while it expands its body, creating space for future growth, before the new armor hardens. This hardening process can last from several hours to a few days. Only once the new cuticle is fully sclerotized will the spider emerge to resume its normal activities.