I'm playing SoulSilver and I want to catch a Heracross.I'm using headbutt at the trees in route 42, but no Pokemon appears.Why ?
You might be using Headbutt on the wrong tree. But, if you're damn sure, you're doing on the right tree, I'll tell you what, if you headbutt a tree and it does not cause a wild Pokémon to attack, then this tree will never have any Pokémon on it. If the tree does have a Pokémon come out, this tree will always have a wild Pokémon encounter when you headbutt it
Linked to Serebii's guide to headbutt