why dose this exist

for me, I really do not know why mosquito exist. I do not like it, there are some reason for this. first of all, it is no useful for something. it just flies everywhere and make me feel so bad. secondly, it can transmitted diseases when it eats people's blood. a lot of ill are from mosquito. thirdly, it makes people feel itch when the people got bit. indeed, i think there should be no mosquitoes.