Look on leaves, particularly of a caterpillar's favourite food plant e.g. cinnabar moth caterpillar on ragwort. Also look for signs of their feeding, for example chewed leaves and even their tiny black pellets of poo (frass).
Butterflies and moths transform during their lives, with their young looking very different from the adults. This transformation is known as complete metamorphosis. In this, the insect goes through four distinct stages: egg, larva, pupae/chrysalis, then adult. A caterpillar is their larval stage. They come in all shapes, colours and sizes. Some are hairy with poisonous itchy hairs for protection, others are camouflaged to look like leaves and twigs while others are brightly coloured as a warning that they are poisonous.
Basically caterpillars are stomachs with legs and their job is to eat as much food as possible! Although they are insects and so only have six true legs, you can be fooled into thinking they have more because they have developed eight ‘pro legs’ further down their body.
Pupa is the word used for the stage before all caterpillars becomes adult, during which they are contained in and protected by a hard covering. However, a chrysalis is only used for butterflies. The word means ‘golden’ and refers to beautiful metallic sheen found on some.