The Butterfly Life Cycle
Insects develop in two different ways to reach their adult form. Some, like stick insects and grasshoppers, undergo three stages during their life cycle. Nymphs hatching from the eggs already resemble the adult version. As they grow, the 'only' thing they do to become an adult is to shed their exoskeleton and emerge with a new skin, a process that is repeated until they have reached adulthood. Others like dragonflies and damselflies spend their larval stage under water only to emerge when ready to shed their skin for the last time and to take on their adult shape.
The life cycle of butterflies and moths is different. Just like bees, flies and beetles they undergo four different stages and completely change their appearance ever time. This transformation visible in the main image is called metamorphosis.
After mating the female butterfly deposits her eggs on the larval host plant. The Orchard Swallowtail places single eggs on leaves, others like the Caper White lay them in clusters. Come butterflies choose the underside of leaves, others like the Orchard Swallowtail deposit their eggs on the upper surface. Each egg is ca. 0.5mm in diameter.
From each egg a tiny caterpillar (larva) emerges. The one of the Orchard Swallowtail looks like a brown-white bird dropping at first, which may well be excellent camouflage. The caterpillar uses the eggshell as its first food source. The chewing mouth parts (mandibles) of the larva are subsequently used to feed on leaves of the larval host plant. The weight of any caterpillar multiplies many times after it emerges from the egg. Each time is outgrows its skin, it moults by splitting it and emerging with a new one. Moulting happens four times for the Orchard Swallowtail. The stages between these molts are called instars. Larvae may change colour over time.
At the end of the fifth instar stage, when fully grown, the caterpillar stops feeding. It attaches itself to a branch or branchlet of the larval host plant, sometimes also to the underside of a leaf via a stem-like appendage, supported by a girdle spun from silk. It then pupates.
While in the chrysalis (pupa) and without it being visible from the outside, body tissues are being rebuilt until the caterpillar has transformed into an adult butterfly, ready to emerge and to open its wings, to dry them and to then start the life cycle again by finding a mating partner.