Bear hunter dmg calculation

When is the dmg of the trap calculated? On placement or on trigger?

On placement!

is there a max number for traps exissting at same time?? if yes, how is it counted? per pathtile? per bearhunter? global?

You can test it through 2 bear hunters support towers (second one build with a delay), away from carry who kill everybody and not allowing to approach to bear hunters