Walkthrough
Located in the center of Route 2 is Viridian Forest. Here, loads of Wild Pokemon (primarily Bug Types) and Pokemon Trainers (who also like to use Bug Types) can be found. You must make it through Viridian Forest in order to make it to the other side of Route 2 on your way to Pewter City. There, the first Pokemon Gym can be found.
Wild Pokemon
Grasses:
Caterpie (40%): Levels 3-5
Weedle (40%): Levels 3-5
Kakuna(FireRed)/Metapod(LeafGreen) (10%): Levels 4-6
Metapod(FireRed)/Kakuna(LeafGreen) (5%): Level 5
Pikachu (5%): Levels 3-5
Pokemon Trainers
Bug Catcher Rick: Level 6 Weedle, Level 6 Caterpie
Bug Catcher Doug: Level 7 Weedle, Level 7 Kakuna, Level 7 Weedle
Bug Catcher Anthony: Level 7 Caterpie, Level 8 Caterpie
Bug Catcher Charlie: Level 7 Metapod, Level 7 Caterpie, Level 7 Metapod
Bug Catcher Sammy: Level 9 Weedle
Items
Poke Ball: On Ground
Antidote: On Ground
Potion: On Ground
Potion: On Ground
Antidote: ItemFinder
Potion: ItemFinder