It's not fun...dealing with Insect-type Demons.
They're gross and yucky even for a battle-hardened Ashton. Their piercing screeches hurts his ears and every time he shoots them, their bodies always make that skin-crawling, gross, squelching sound which is just...no.
The tunnel network was bigger and airy than what he initially expected. It's smelly too, so much that Ashton had to wear a respirator since he just didn't want to deal with that.
A few things in his initial plan didn't work.
For starters, insect-type demons are uncannily perceptive, they practically sensed him the moment he stepped foot in the tunnels.
He didn't get 'mobbed' per se, since there weren't a lot of insects roaming around this particular area anyway. However, there are enough of them to make him sweat a bit.