i don't have this issue to the same extent that the author of the original post has mentioned, but i can relate to this.
there is (or was) a folk belief in at least some areas of russia that killing a house spider is wrong, and it has always resonated with me. i feel it is wrong too, somehow. i think this might be connected to a memory from my earlier childhood (one of the very few that i have) - i remember being in the forest with my grandfather, to whom i was very close, and playing in a small natural sandpit where the roots of some pine trees came to the surface and were suspended a few inches above the country road. i would dig the sand with a little spade or just sift it through my fingers and feel its texture. there were quite a few daddy-long-legs living there and occasionally they would scurry out once i disturbed the sand. my grandfather used to take them into his hands and tell me that they were beautiful beings, with those long delicate legs of theirs; his entire face would light up as he said this, and he handled them immense care (he was a radiant, genuinely loving person).
i'm nothing like him, but i want to be and i think this memory might be the reason why i feel bad about killing spiders or spider-like creatures in particular. if i see a house spider at a place where it might give me an unpleasant surprise (i have been phobic of spiders until fairly recently and some remnants of the old feeling surface from time to time), or where my cats could kill it, i transfer it onto a slip of paper and to some remote corner. i try to save the butterflies or moths that find themselves in the apartment by mistake - if i can catch them without the risk of rubbing the dust/scales off their wings, i do so, or i open the window as wide as possible and hope they find their way out before my cats discover them. i won't step on a beetle if i see one crawling underfoot.
it is difficult to explain. i am far from being a vegan (tried to be a non-vegan vegetarian in my mid-teens, failed miserably, not going to go there again), i feel no guilt about eating meat, i wear leather and the fur of animals whose meat i would have eaten if it were available and/or affordable, such as rabbits. i'm fine with people who hunt, though i would not have done this myself - yes, i buy my food at a store and have someone kill animals for me, whereas they obtain their food directly and kill their own animals, but i see no great difference between those two choices. and i don't really mind my cats killing small animals on the whole because this is what they are supposed to do as predators, regardless of whether or not it makes humans uncomfortable. that said, i still do not like killing insects. i simply do not.
i think one other reason could be that i find them thoroughly fascinating. i can stare at their photos for hours (could stare at live ones too, but they are not going to pose for me
). so i guess it feels wrong to destroy one of those pieces of god's handiwork that are so intricately structured, awe-inspiring and intensely
other. i wouldn't know how to explain it otherwise.