A pupa is the life stage of some insects undergoing transformation between immature and mature stages. Insects that go through a pupal stage are holometabolous, meaning they go through four distinct stages in their life cycle: egg, larva, pupa, and imago. During pupation, larval structures break down, and adult structures such as wings appear for the first time. The pupa is the stage between the larva and adult stages. The pupae of different groups of insects have different names such as chrysalis for the pupae of butterflies and tumbler for those of the mosquito family. Pupae may further be enclosed in other structures such as cocoons, nests, or shells. Pupae are usually immobile and are largely defenseless, so they often cover themselves with a cocoon, conceal themselves in the environment, or form underground. Some species of Lycaenid butterflies are protected in their pupal stage by ants. Another means of defense by pupae of other species is the capability of making sounds or vibrations to scare potential predators. A few species use chemical defenses including toxic secretions.