They're vectors for a whole host of diseases, but we can hardly aim to eradicate them (we probably wouldn't be able to even if we wanted to and then ethical concerns suggest we mustn't go down that route). I went to Mexico last summer so to be on the safe side the balcony door (with a mosquito curtain behind it) was always slid shut. I had two bands on my wrists. They seemed to work for me - I only got bit once. In the past, without the bands, they've used me for target practice.