Just before they pupate, monarch larvae will spin a small silk button, or pad. The larvae will then hang upside down from this pad by their last pair of prolegs, assuming the J-shaped position of the prepupa. The silk comes from the spinneret on the bottom of the head. As it sheds its skin for the last time, the caterpillar stabs a stem into the silk pad to hang. This stem extends from its rear end and is called the cremaster.