The short answer is, as you might guess, "a lot."

But the long answer is kind of crazy.

There are more than 3,500 species of mosquitoes, all of varying sizes, appetites, and dispositions. So the (very large) number varies depending on the kind of mosquitoes descending upon you in one dense, bitey cloud.

However, let's use the Asian tiger mosquito as our human-draining insect. It's a common biter in North America and a "bad guy" invasive species there.

So how many of those mosquitoes would it take to completely exsanguinate a human?

One female (males only eat nectar) will typically drink about five microliters of blood in a meal, Zach Adelman, an entomologist at Virginia Tech, told Tech Insider in an email. That's roughly the volume of a single dried mustard seed.

Now consider the average human has 5.5 liters of blood, or 5.5 million microliters.

If you do the math, you'd need a swarm of 1.1 million Asian tiger mosquitoes to completely drain a human's blood — but chances are you'd die long before all your blood was gone.

A condition called hypovolemic shock sets in after you lose about 20% of your blood, and it leads to major organ failures because your heart loses the pressure necessary to circulate blood.

Another thing to consider is the amount of skin a human has for the mosquitoes to bite. An average person has about 1.75 square meters of skin. That means you'd need almost 6,300 Asian tiger mosquitoes feeding on each square centimeter of skin on your body.

So unless they set up an orderly queuing system to get at your skin, there's little to no risk of having your blood drained by mosquitoes, let alone encountering a swarm of millions. But mosquitoes are not necessarily the most profilic bloodsuckers.

"The only bloodfeeding insect that may come close is the blackfly," Michael Riehle, an entomologist at the University of Arizona, told Tech Insider. "They consume about the same amount of blood, but some of the larger rivers can produce millions of blackflies per square meter."