A caterpillar does not fully dissolve into soup inside its cocoon
The popular image of a larva melting into liquid inside its case is wrong. During the pupal stage, larval tissues are broken down while adult structures grow from clusters of cells called imaginal discs. The pupa, named from the Latin for doll, can last days or years, and fleas wait inside for a host's vibrations.
Insects with complete metamorphosis, the Holometabola, pass through four stages: egg, larva, pupa and adult, or imago. Hormones such as juvenile hormone and ecdysone govern the transition into and out of the pupa. Becoming one is called pupation; breaking out is eclosion. Names differ by group: a butterfly's pupa is a chrysalis, a mosquito's a tumbler.
Most pupae neither eat nor move, anchored in place until transformation is done, though mosquito pupae are strikingly active. Duration depends on species and temperature; monarch butterflies spend eight to fifteen days as pupae, while others enter dormancy, called diapause, until the right season, over winter in temperate lands or through the dry season in the tropics. Just before emerging, the adult inside is termed pharate, and the empty case left behind is the exuvia, so flimsy in ants, bees and wasps that it crumples as it comes off.
Timing of emergence follows internal clocks in many species, which interests chronobiologists. Most butterflies break out in the morning, mosquitoes in the evening or at night. Being largely helpless, pupae defend themselves in varied ways: cocoons, camouflage, burial underground, toxic secretions, or sounds and vibrations to deter predators. Some lycaenid butterflies are guarded by ants, and social insects protect their own pupae in the hive. In a few butterflies, notably Heliconius, males mate with females still in the pupa or just emerged, then seal the female with a plug called a sphragis or mark her with an anti-aphrodisiac scent.
Entomologists also sort pupae by their jaws. Decticous pupae have working mandibles for cutting free, as in lacewings, scorpionflies and caddisflies. Adecticous pupae lack them, including beetles, flies, fleas and the wasp and bee order Hymenoptera.
Source: Pupa
