I fucking hate mosquitos and flys, dirty beasts! i heard that something like 10-15 years ago there were almost no mosquitos in my city, then i dunno what happened, i blame Radament, he probably brought those nasty insectoids here.
Generally i let spiders live, if they build a web on my ceiling i guess it's because they can catch some insects, so they can maybe help a bit to keep my house mosquitos/flys free in summer. Moreover, i have never been bitten by spiders, well except once, but that's because i accidentally broke a spider's web with my hand/arm while i was riding a motorbike, probably because i was riding too close to the right border of the road.
I remember i felt a bit of pain and itch, like a sting or something, so i stopped my mbike and i saw a spider on my hand ( which i immediatlty removed). Shortly after the bite "wound" become like some sort of bubble, which i pierced/scratched and some white-ish liquid came out of it, i guess it was the spider's "poison" or a reaction to it.
I also let scorpions live (the few times i found one of them in my house), i killed 'em when i was too lazy to put 'em back into my garden, scorpions probably eat only nasty insectoids and they don't sting/bite humans unless you try to catch 'em with your hands or you accidentally step on one of 'em barefooted.
Here's a scorpion i "captured" 4-5 years ago, i took a couple of pictures and then i realesed it back into my garden. I put a piece of ham in a box to see if the scorpions would eat it, but the arachnid was not interested

.