Molting is a biological process in which spiders (and other invertebrates) shed their exoskeleton – the flexible outer covering of their body – and form a new, larger covering during their developmental stages.
Why do Spiders Molt
Spiders shed their skin simply to grow in size. They have an exoskeleton, which is quite strong due to the presence of various protein molecules, and a long-chain polysaccharide called chitin. Although this structure is flexible enough to allow the spider to move, it does not expand or grow as the spider’s internal organs do. Therefore, spiders need to form a new exoskeleton and shed the old one so that they can increase their size.
Spider Molting
How Often do They Molt
Young, growing tarantulas, for example, molt once a month while the adult ones may shed their skin every year or two. Brown recluse spiders usually molt five to seven times before growing to its full size. House spiders too molt repeatedly during their growth stages.
Do All Spiders Molt
All spider species are known to molt several times throughout their life cycle.
How do Spiders Molt
The molting process is initiated with the release of hormones by the spider’s body. As the spider starts shedding its skin, the inner elastic layer of the exoskeleton is first broken down, followed by the reabsorption of its nutrients. Meanwhile, the outer layer stays intact until the new, larger exoskeleton is ready. The new, folded exoskeleton will start expanding after the spider sheds the old one.
The spider cracks the old exoskeleton by increasing its heart rate and pumping more blood into its cephalothorax, thereby expanding its body. Next, the spider flexes its muscles to push itself out through the crack. As the spider takes in air, it creates more space in the newly-formed, soft exoskeleton, which allows for its growth. The molting process gets complete when the exoskeleton hardens and attains its firmness.
Spiders need to molt because their exoskeleton, a rigid outer covering, does not expand as the spider grows. To increase in size, the spider must shed this restrictive shell and form a new, larger one. This process is essential for the spider to accommodate its growing internal organs.
A spider starts the molting process through the release of specific hormones. These hormones trigger the breakdown of the inner layer of the old exoskeleton, allowing the spider to reabsorb its nutrients. Meanwhile, a new, larger exoskeleton begins to form underneath the old one in preparation for shedding.
The frequency of spider molting depends on the species and its age. Young, growing spiders molt more often; for example, a young tarantula may molt monthly. As spiders mature and their growth slows, the frequency decreases significantly, with adult tarantulas sometimes molting only once every one or two years.
To crack the old exoskeleton, a spider intentionally increases its heart rate to pump more hemolymph (blood) into its cephalothorax. This rapid increase in internal pressure causes the spider’s body to swell, which forces the old, brittle exoskeleton to split open, allowing the spider to emerge.
Yes, spiders are extremely vulnerable immediately after molting. Their new exoskeleton is very soft and offers little protection until it hardens, a process that can take several hours or days. During this time, the spider is susceptible to predators and physical injury due to its soft, pliable body.
Yes, all known spider species molt several times throughout their lives. Molting, or ecdysis, is a fundamental biological process required for growth in all spiders and other arthropods with exoskeletons. The number of molts may vary, but the process itself is universal across all spider species.
A spider’s new skin hardens after it has fully expanded to its new size. Once the spider has emerged, the new, soft exoskeleton is exposed to air. A chemical process called sclerotization then occurs, where proteins within the cuticle cross-link, causing it to progressively harden and darken.
