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.
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.
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.
All spider species are known to molt several times throughout their life cycle.
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.
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