This is the same kind of anxiety I have. This sounds a lot like OCD or an anxiety disorder. Consider the following: thoughts can not be immoral, actions can be. Your mind is your own playground to do whatever you want in, and if the thought of killing bugs is what comes into your mind, thats merely you experimenting with the idea. It says nothing about your character besides your curiosity. There's a reason why thoughtcrime has historically been an idea in dystopian novels: our thoughts are not entirely in our control. We can vaguely guide the flow with some willful control, but the river will flow whether we like it or not. Don't shame yourself for your brain functioning exactly as it should. We have ideas and then we crosscheck those ideas with what our ideal self would be. Your ideal self would disapprove, as evidenced by your concern over this. It is admirable that you clearly care so much for your wellbeing, but the energy is misplaced. The more energy you put into the moral value of these mere thoughts, the more valid they will seem to your brain. Intrusive thoughts are ultimately uncomfortable, but they have no power over you unless you give them it.

note: most people dont give a shit about bugs, me included. the urge to get rid of a bug or other small invertebrate is totally normal. if having these thoughts makes you a murderer... then everyone else is genocidal.

This sounds like OCD. You might want to seek psychiatric help.

Well, it's s loooong road of escalatiion from invertebrates to humans, so by the time you work your way up, you'll be too old to be good at killing humans, so you'll get caught easy.

I need you to think carefully before you answer:

Have you killed any human beings?

I think that's where folks start, when figuring out of they're prone to serially killing.

bugs, slugs, snails, etc. really bother me

Usually there's a specific reason in our memories why specific creatures bother us. That said, the ones you mentioned bother pretty much everyone, so you're in good company.

It should only be concerning if you find you like torturing them, and you start escalating to other animals.

Some early signs of psychopathy are torturing small animals, like cats and squirrels. Something to do with a lack of empathy.

If you can remain content to simply murder slugs and other crawlies that invade your domicile, then you're not a danger to anyone.

You are so sweet. Don’t worry about it.

I often kill bugs when I see them. I don't like them. Most people are like this. Yet we are not serial killers. Bugs suck. Only some weirdos like entomologists and other related dorks (I am using words like "weirdos" and "dorks" lovingly, as I am a different flavor of said descriptions lol) love them! It's perfectly natural to hate all bugs imo. I wouldn't be surprised if we are genetically predisposed to dislike them because of how they spread disease.