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Caterpie is a serpentine Pokémon that resembles the larvae of the Spicebush Swallowtail. It is a green caterpillar with yellow ring-shaped markings down the sides of its body. It also has large yellow eyes with black pupils. Its most notable characteristic is the bright red antenna (osmeterium) on its head, which releases a stench to repel predators. These and the large eye-shaped markings help to startle predators. Its feet are tipped with suction cups, permitting this Pokémon to scale most surfaces with minimal effort.
Caterpie 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 Ash Catches a Pokémon. It has a voracious appetite that causes it to eat leaves larger than itself. It primarily feeds on vegetation, such as tree leaves. According to Pokémon Adventures, its favorite food is the Vermilion flower. Caterpie lives in forests.