All crustacea must replace their exoskeletons with new ones in order to grow. They replace their exoskeletons by moulting. Moulting is controlled by hormones. A new exoskeleton is then secreted to replace the old one. While they wait for their new exoskeleton to harden it can be dangerous. They may be preyed on by larger predators and not be able to defend themselves. Most crustaceans moult many times between hatching and adulthood. 