How do you catch acarus in Pokemon soulsliver?

You can't catch Acarus in Pokemon Soulsilver. Acarus is not a Pokémon in the Pokémon universe. It's possible you're thinking of a different Pokémon with a similar name, or you might be referring to a creature from a different franchise.

Could you please clarify what Pokémon you're interested in catching? I can help you find information on how to catch it in Pokémon Soulsilver.