Jumping spiders (family Salticidae) are recognized by their large, forward-facing eyes and characteristic hunting style that relies on quick, precise leaps. Like all arthropods, these active predators possess a rigid outer shell that does not expand as they grow. Shedding this exterior, known as molting, is a fundamental, recurring process necessary for their development and increase in size. This process enables them to transition through various developmental stages.
The Biological Necessity of Shedding
The physical constraint that makes molting necessary is the spider’s exoskeleton, a hard, inelastic outer layer called the cuticle. This external skeleton provides structure and protection, but it prevents continuous growth. To accommodate an increase in body mass and size, the spider must periodically shed this restrictive shell through a process known as ecdysis.
Molting is the only biological mechanism that allows a spider to increase its size, providing a new, larger “suit” of armor. Between each successful molt, the spider is in a developmental stage called an instar. Younger spiders molt more frequently, sometimes every few weeks, because their growth rate is rapid.
The shedding process also serves a restorative function, allowing the spider to repair damage or regenerate lost limbs. A lost leg may appear as a small stump after one molt, but it will gradually grow larger and more functional with each subsequent ecdysis. The number of molts varies by species and gender, but it occurs between six and nine times before the spider reaches full maturity.
Observable Stages of the Molting Cycle
The entire process of ecdysis is divided into three observable phases, starting with the preparatory stage known as pre-molt. During this time, the spider’s behavior changes noticeably; it often refuses food and becomes less active. The most distinct sign of pre-molt is the construction of a dense, opaque silk sac or “molting hammock,” which serves as a safe, secluded retreat.
Inside this retreat, the spider secretes a fluid between its old exoskeleton and the forming new one, chemically separating the layers. The actual shedding, or ecdysis phase, begins when the spider lies on its back or side to push its body out of the old skin. The old cuticle, or exuvia, typically splits near the cephalothorax, and the spider slowly pulls its legs and abdomen free. This is an intensely vulnerable time, as the spider is temporarily defenseless and the process can take minutes for a young spider or several days for a sub-adult.
Once free, the spider enters the post-molt phase, where the new exoskeleton is soft, pale, and flexible. This soft-bodied state is referred to as “teneral,” and the spider remains inactive within its hammock. The new cuticle must harden, or sclerotize, which can take several days to a week, depending on the spider’s age and size. The spider uses internal fluid pressure to expand its new body before hardening is complete, ensuring the new exoskeleton is larger than the one just shed.
Environmental Needs During Shedding
Maintaining the correct environmental conditions is important for a successful molt, with humidity being the most influential factor. Adequate moisture levels, generally between 50% and 80%, help ensure that the old exoskeleton remains pliable and does not dry out, preventing the spider from becoming fatally stuck. Misting the enclosure sides provides the necessary humidity and offers water droplets for the spider to drink, as proper hydration is also necessary.
During the pre-molt and active molting phases, all live prey must be removed from the enclosure immediately. Feeder insects, such as crickets, can injure or kill a spider that is preparing to molt or is soft-bodied and defenseless in its hammock. Disturbing the molting hammock should be avoided, as the spider relies on this secure structure for the duration of the process.
The spider should not be offered food until the new exoskeleton is fully hardened, which requires waiting several days after shedding. Feeding a spider too soon can damage its still-soft fangs and mouthparts, leading to injury. Once the spider emerges from its retreat and begins moving normally, it is safe to resume its regular feeding schedule.