Spiders and other arthropods don’t have skeletons inside their bodies like vertebrates do, but they do have exoskeletons outside their bodies to protect the soft parts inside. This means they don’t have to worry about broken bones.
However, there is one fatal flaw to this design. Whenever arthropods get bigger, their exoskeletons do not grow with them. Instead, they need to shed their smaller, older exoskeleton in order to grow into their newer, bigger one underneath.
Watch what happens when this tarantula molts its old exoskeleton:
As if we needed another reason to be creeped out by spiders! But let’s set aside our fears for a moment and replace them with wonder. When spiders molt, the process is called ecdysis. Before undergoing this tiring process, spiders will stop eating several days. Once they shed their hard outer shell, they are completely exposed. While their new exoskeleton hardens over the next few hours, their bodies are soft and vulnerable.
Unfortunately, this is not a one-time process. Spiders will molt between five and nine times before reaching maturity; however, males have it a little easier. Since male spiders are generally smaller than females, they often don’t need to molt as many times as females before reaching maturity.