They were either gathered like mere paper, or not just a small group of about a dozen individuals.
When their numbers exceed hundreds, or when thousands or tens of thousands of monsters cluster like an insect army, a powerful leader is naturally needed for that group to function properly.
Just as there's a silver monkey in the primate group, there's a swamp monster in the insect army.
But an organization can't function with just a leader.
If a group has a certain scale, it needs an advisor to realistically carry out the leader's will.
The advisor of primate monsters is called the 'sage', an old orangutan.
The orangutan didn't become an advisor because of its strength.
It's because of its high intelligence and excellent language skills.
And the insect army also had an advisor.
He was a spider.
A Demon Face Tarantula.
A monster with a demon's face floating on its plump belly.
