Why am I so afraid of bugs?

Every time I see one I run to my room and lock the door.I close all the windows.Close all the shades of the windows.And you know that skinny hole under your door.I cover it with blankets.I do all the stuff so that it doesn't touch me or bite me.I OD *I go way over the top*..I am even afraid of butterflies.Even if I see a like passed away one.I like still freak out.It just looks gross,weird and creepy,Why do I do this?What do I have to do to stop?Please help me.Ty :)