It would take 12,00,000 mosquitoes sucking at once to completely drain a human of blood.
Must be a good few millimeters gone! “Amosquito on average will suck five millionths (0.000005) of a liter of blood. So dividing, it would take 5/0.000005 = 1,000,000 mosquitos to drain all five liters from the human body.
What attracts mosquitoes to bite you?
Finding someone to bite. Mosquitoes are stimulated by a number of factors when seeking out a blood meal. Initially, they’re attracted by the carbon dioxide we exhale. Body heat is probably important too, but once the mosquito gets closer, she will respond to the smell of a potential blood source’s skin.