Instructions
Go to the National Park on a Tuesday, Thursday or Saturday to participate in a Bug Catching Contest. The goal of the contest is to walk around the park to find and capture the best Bug-type Pokemon you can find using up to 20 Park Balls. You can find the National Park positioned between Routes 35 and 36 in the classic Game Boy version of "Pokemon Silver."
Walk through the tall grass to find wild Bug Pokemon. Although you will meet all kinds of strange insects, keep an eye out for a shiny Butterfree and its previous evolutionary forms Caterpie and Metapod.
Throw a Park Ball if you meet a shiny Butterfree, Metapod or Caterpie. While a shiny Butterfree will already be pink, you should capture any shiny yellow Caterpie or red Metapod that you find.
If you can capture a shiny Caterpie or Metapod, you can evolve it into a pink Butterfree. Train shiny Caterpie to level 7 and it will evolve into Metapod. Once shiny Metapod grows to level 10, it will become a pink Butterfree.