The caterpillars/butterflies in this episode are based on the Imported Cabbage Worm (Peris Rapae), a common caterpillar that feasts on cabbage as its main diet, along with other mustard-family plants. The Imported Cabbage Worm grows up to be the Cabbage White Butterfly.
Goof: The caterpillars could not have completed their transformation into butterflies in just one night; during the night they go into pupation, and emerge as butterflies the next morning. In real life it takes at least a week for a caterpillar to change into a butterfly or moth when it is in the pupa stage (some butterflies may spend the whole winter pupating if they are caterpillars in the fall).
The kids' costumes for Goblin Night:
Little Bear: A monster
Cat: A black cat
Owl: A ghost
Duck: A thunder cloud
Mitzi: A goblin