Why are people so afraid of flies, spiders, and bugs?

I’m speaking for myself and a lot of other women and people I know.

I’m wondering about the fears and psychology behind this -

When even an adult has fear against a teeny-tiny, seemingly harmless little spider or insect. Why do people get scared, even though they clearly know it is JUST a small spider… ? Where does it come from?

I was walking in my room and I came across what I had thought to be a spider or small black bug on the floor. I jumped back and then realized it was just black cloth… What made me jump back so scared ? It wasn’t like I was seeing a murderer in front of me, how can people (especially girls) be so creeped out of bugs ?