Caterpie is a Pokémon that resembles a green caterpillar with a yellow underside and teardrop-shaped tail. There are yellow ring-shaped markings down the sides of its segmented body, which resemble its eyes and are meant to scare off predators. Its most notable characteristic is the bright red antenna (osmeterium) on its head, which releases a stench to repel predators. Despite these features and its camouflage in green foliage, Caterpie is often preyed upon by Flying-type Pokémon. Its four tiny feet are tipped with suction cups, permitting this Pokémon to scale most surfaces with minimal effort.

Caterpie is easy to capture and grows quickly, making it ideal for new Trainers.

As Caterpie grow and develop over time, it will shed its skin many times before finally cocooning itself in thick silk. It can also spit this silk in order to entangle foes as seen in the anime. It has a voracious appetite, which drives it to eat a hundred leaves a day. It will even eat leaves bigger than itself. According to Pokémon Adventures, its favorite food is the Vermilion flower. Caterpie lives in temperate forests and jungles.