The Caterpillar or Larva...
Butterfly caterpillars or butterfly larvae are the main feeding stage of the life cycle of butterflies, and have been described as food processing machines with their main functions being eating and growing.
They are very particular in their feeding habits, feeding usually only on a small number of closely related plants.
The butterfly larvae feed mostly on the leaves of flowering plants and trees, and if present in large enough numbers can defoliate large areas of vegetation. In this way larvae that feed on agricultural crops can be serious pests.
As the larvae feed and grow they entirely fill their skin, which does not stretch and so becomes very tight. In order that growth can continue, this skin is shed revealing a new larger one beneath. This shedding of the skin or moulting takes place four or five times before the butterfly larvae reach full size.