Butterflies have a complex life cycle with distinct stages of metamorphosis. They begin life as small eggs laid on plant stems or leaves. Typically, it takes a few weeks to hatch, but some eggs only hatch when the temperature reaches a certain level. The benefit of the egg location is that the larvae, known as caterpillars, have plenty of food in their immediate vicinity.
Caterpillars are voracious eaters, taking in a variety of plant materials as they expand to a size around 1,000 times birth weight. As the caterpillar grows plump, it molts or sheds its skin four or five times. While most caterpillars grow beyond the larval stage in a few weeks, some, such as the wood-eating carpenter worm, require years to do so.
The seemingly excess calorie intake is actually preparation for one of nature’s most dramatic transformations. While nearly all insects go through larval stages en route to gaining wings and adult appendages, the caterpillar uses a cocoon, or its own exoskeleton, as a casement in which to break itself down at a cellular level and ultimately emerge with a new form.
On the day it stops eating, the caterpillar hangs from a leaf or twig and spins a silky cocoon around itself. Alternatively, it molts, shedding its skin one final time. This forms the protective chrysalis in which the caterpillar undergoes changes as a pupa (intermediary stage between larva and adult insect). Within the cocoon or chrysalis, the pupa is actually releasing enzymes that dissolve its tissues, as it essentially digests or feeds on itself. This is readily apparent from the soupy liquid that oozes out when a cocoon or chrysalis is opened at a certain stage in its metamorphosis.
The pupa is not exactly the shapeless mess it appears to be, however. Imaginal discs, or highly organized cells, make it through the digestive process. These imaginal discs, one for each adult body part, are actually created within the egg at the earliest stages of the life cycle. In the caterpillar stage, these either lie dormant or take their adult shape as tiny appendages within the exoskeleton.
After the caterpillar has disintegrated its tissue, with the exception of the imaginal discs, these discs go to work. They consume the surrounding soup, rich in protein, to achieve rapid cell division. Elements such as the antennae, wings, legs, eyes, and genitals take shape, with sections of the nervous system and muscles expanding. Cognitive carry-through may even occur, with one study of adult moths revealing that they seem to remember events that happened when caterpillars.
When the adult butterfly finally emerges from its exoskeleton, it takes to the sky on newly formed wings. Much of its adult life, which often only lasts a few weeks, is spent searching for a mate so that a new batch of eggs may be fertilized and the butterfly life cycle continues.
One of the unique items at the Smoky Mountain Relic Room in Sevierville, Tennessee, is a series of cases displaying mounted butterflies of various sizes and vivid hues. These are ethically sourced from an arboretum in Peru, with those butterflies that didn’t make it through the night collected by villagers each morning and preserved as natural works of art.
