While Pandavas were on Vanvas
Bheem had been always on his guards. He would go on poaching, kill dangerous animals who could pose danger to sages and locals.

He would kill the Demons residing in the area
He had even fought with Gandharva & Rakshas army guarding garden of Kuber.

Do you know why?

Here is my perspective.
Bhim knew that the great war was coming.
It was his duty to punish those criminals who had cheated his brother.
Who had stole all what Pandavas had.

He knew he didn't had the divine weapons which Arjun had.
He had his power and stamina which was his own and also from gift of Nagas.

We must keep ourselves prepared for the situation which we are going to face in near future. With power, intellect & knowledge. At even in front

Europe is facing it today.
We are also facing it in bits and pieces. The doom's day is near.

Prepare or get defeated. Defeat means extinction.

The choice is yours