Ash caught Beedrill in the Bug-Catching Contest in The Bug Stops Here. In catching it, he won the contest, and, according to the rules, the winner is allowed to keep the Pokémon that was caught. However, Ash chose to give Beedrill to Casey afterwards because of her love for yellow and black-striped Pokémon. It has since become one of her three main Pokémon, along with Meganium and Elekid.
Due to appearing only very shortly before being caught, Beedrill's original nature remains uncertain, although it was shown possessing aggressive characteristics typical to its species while attacking Ash. After joining Casey's team, it seems to have adopted Casey's confident and cheerful attitude, eagerly joining Casey, Meganium, and Elekid in performing the Electabuzz theme song.