Mothim tree?

[Guest Relinquished]

I was in Aventurine woods, south i think and while hunting for WORMADAM, i found a MOTHIM, accidentally at that, at very first Headbutting attempt, too... No pokeballs on me, so i left. I returned, got myself the wormadam i had been seeking initially, but... No Mothim, this time round... I searched many trees on many places, but only Wormadam dropped.

 

Any ideas? What trees are the correct ones? Wiki says "low encounter" ones, but i don't know what that means. And always wormadam appears...

[logintomylife]

When you headbutt a tree something happens like, let's say, throwing a dice. On each number you face different pokemon, that is happening here, too. You just need to keep headbutting till you encounter it, it's about a chance, not about the tree.