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I'm just curious, how many mosquito "bites" (mosquitoes which have removed blood from a person) would it take to remove enough blood to put a person into shock? (Putting aside all reasons why it wouldn't happen, how many would it take?)

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    $\begingroup$ I don't have any mosquitos on hand to test this, but lets assume an average mosquito has a carrying capacity of 50uL of blood. If the average human has 8L of blood, 8 million uL / 50uL is 160,000 mosquitos. That's probably a decent first order approximation. I don't know how much blood a person has to lose before they go into shock, and that 50uL per mosquito estimate is based only on what I remember a full mosquito looking like, but I've never been good at measuring volumes by eye. $\endgroup$ – user137 Jan 5 '15 at 21:44
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    $\begingroup$ @user137 I don't know about your mosquito numbers, but 8l of blood sounds very unusual. I've always thought that the average is 4-5. Else, good starting point for the calculation. $\endgroup$ – rumtscho Jan 5 '15 at 21:54
  • $\begingroup$ @rumtscho You're probably right, I just remembered hearing somewhere that a human had 8 quarts of blood and 1 quart is about 1L. $\endgroup$ – user137 Jan 5 '15 at 22:09
  • $\begingroup$ @user137 Chris's approach sounds right - estimating the amount of blood based on body weight. Maybe you encountered the 8 quarts figure in a text on obese patients. I already thought after leaving the comment "wait, there's no way everybody has the same amount of blood". $\endgroup$ – rumtscho Jan 5 '15 at 22:24
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    $\begingroup$ You might have to factor in blood loss after the Mosquitos leave due to the anticoagulants they inject. Unless we're talking 200k Mosquitos at exactly the same time... Great, that's my sleep gone for tonight. $\endgroup$ – user12869 Jan 7 '15 at 12:12
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This question falls into different subquestions:

1. How much blood does a mosquito take when feeding?

This is not so easy to answer, but there are publications which measure the volume of different mosquito species. Reference 1 lists volumes between 2.85 and 11.99µL per meal and mosquito. Reference 2 lists 3.07 and 5.71µL. To make the approximation a bit easier, let's assume that mosquitoes drink about 5µL per bite (which should be near enough).

2. How much blood does a human have?

According to Wikipedia, humans have around 77mL blood per kilogram of body weight. If we take a 70kg human, we get around 5L of blood.

3. How many mosquitos does it take to get a human into shock, and how many to suck him out completely?

According to the Medline, Hypovolemic shock occurs when a human loses about 1/5 (or more) of his blood volume. 1/5th of 5L is one litre. Since each mosquito sucks 5µL, this would take about 200.000 mosquitoes. To suck out all blood would take 1 million mosquitoes. (This is not possible since mosquitoes depend on an existing blood pressure, as reference 3 shows. If a capillary is empty due to massive blood sucking, they change to another.)

Besides this theoretical (but interesting) calculation, there are some real problems about getting biten by so many mosquitos. First, this is a question of available skin. The human skin is about 2 square meters in size, which would require 100.000 bites per square meter. To break this down further, a square meter has 10.000 square centimeters, so there would be 10 mosquitos which need to bite you per square centimeter. Rather unlikely.

Then each mosquito injects a mix of anti-coagulants, pain killers etc. prior to sucking to keep the blood from clotting and also to make sure you won't notice the bite immediately. As pointed out in the comments, this would already cause a lot of trouble and probably cause massive bleeding, since the effect of the anti-coagulants would sum up when biten by thousands of mosquitos. Additionally the body reacts by releasing histamines and since the amount would also be massive, this would cause real trouble and probably kill you.

References:

  1. Regulation of blood meal size in the mosquito
  2. La Crosse Virus Infection Alters Blood Feeding Behavior in Aedes triseriatus and Aedes albopictus (Diptera: Culicidae)
  3. Visualizing Non Infectious and Infectious Anopheles gambiae Blood Feedings in Naive and Saliva-Immunized Mice

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    $\begingroup$ This reads like what-if.xkcd.com. $\endgroup$ – mskfisher Jan 6 '15 at 13:28
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    $\begingroup$ This question would clearly fit there. My drawing skills are less developed, though. :-) $\endgroup$ – Chris Jan 6 '15 at 13:36
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    $\begingroup$ I wonder whether the anticoagulants from 200K mosquito bites would cause more problems than the loss of blood. $\endgroup$ – Jeremy Stein Jan 6 '15 at 18:00
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    $\begingroup$ @JeremyStein: indeed, it seems likely you'd be poisoned somehow before passing out from blood loss. The histamine system would be berserk, for example. Fortunately that's not the question ;-) $\endgroup$ – Steve Jessop Jan 6 '15 at 18:30
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    $\begingroup$ there would be 10 mosquitos which need to bite you per square centimeter. Rather unlikely. Doesn't seem unlikely at all, assuming that they don't all have to be there at once. If a mosquito drinks for 5 minutes at a time, then one mosquito per hour per cm^2 would do it. Images like this one from the Alaskan Arctic make that seem quite plausible. $\endgroup$ – iayork Aug 8 '16 at 19:30
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Everyone seems to forget that the human body replaces blood that is lost quite rapidly. When I donate blood to blood bank they take half a liter or something and I was informed my body will replace it within 30 minutes, I just need to drink plenty of fluid after.

I think it would take a fairly concentrated effort by mosquitoes to do any damage from blood loss.

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    $\begingroup$ Nope, this is wrong. Otherwise blood transfusions would not be necessary, you would only have to supply enough liquids. It takes several days to weeks to fully replace it, see for example here. $\endgroup$ – Chris Jun 6 '17 at 19:05
  • $\begingroup$ It takes several weeks to replace the red/white/platelets yes, but the blood volume is replaced much faster as it is mostly comprised of water. $\endgroup$ – Brian Jun 6 '17 at 19:19
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    $\begingroup$ Hi welcome to Bio.SE! Please provide reputable sources to back up your claims. Anecdotal evidence should be reserved for comments or as supplement to claims supported by trustworthy citations. We ask that all answers on this site provide support, and failure to do so will result in your answer being downvoted or closed. Thanks! $\endgroup$ – theforestecologist Jun 6 '17 at 19:51

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