You remember that plot line in the franchise-killing The Amazing Spider-Man 2: Electro Boogaloo, where mini-Osborn wants Spidey’s blood to save him from looking just a little creepier in a few decades? And Spidey doesn’t want to give it to him because he fears what a transfusion will do?

Not entirely made up for the movie.

For you see, all the way back in 1964’s The Amazing Spider-Man #10, Aunt May needs a post-surgery transfusion, and the doctor wants Peter to donate. Our hero almost refuses, though not because of what it might do to her, but because something in his blood might reveal his superpowers to the world (that’s real selfish, dude).

However, 1960′s medical technology is unable to detect anything, so Pete’s second identity is safe for now. His strength, meanwhile, is weakened for the rest of the comic, so he has to work a bit harder to catch the baddie, who turns out to be a fellow employee of the Daily Bugle named Frederick Foswell.

(He’s a mask-wearing mob boss named The Big Man. JJ thinks it’s Spider-Man. JJ thinks every bad guy is Spider-Man. Spider-Man, meanwhile, thinks it’s JJ.)

Let’s talk about blood.

First, let’s get the “spider blood cells” out of the way. If Peter actually had spider blood, the last thing he’d be worried about is a doctor finding out he has superpowers.

While spiders do have circulatory systems, they function incredibly differently than what you’re familiar with (unless, of course, you study spider anatomy for a living). What you’d call their “blood” is actually a more generic bodily fluid called hemolymph. Like human blood, it’s made of cells and proteins suspended in plasma, but unlike human blood, it’s not different from the fluid that exists between all the various tissues in the body.1

The hemolymph gets pumped by the heart into a cavity called the hemocoel, bathing organs directly with its oxygen and nutrients, and then gets pushed back into the heart. It doesn’t stay in one closed series of tubes going around and around.

This “open circulatory system” requires less energy than a closed one like you or I have, but doesn’t have the high pressures needed to get blood back to the heart particularly fast. So, it wouldn’t work for any animal with an oxygen-hungry metabolism.

In humans, oxygen is transported via red blood cells, which are made up of a protein called hemoglobin. Some arthropods (a classification which includes spiders) use the copper-based hemocyanin instead. It’s dissolved into the hemolymph – rather than existing as “blue blood cells” – and is a much less efficient oxygen transport method than hemoglobin (carrying 17x less). So just like an open circulatory system, it’s probably not the best thing for a warm-blooded, human-sized, super agile spider hero.

The cells that do exist in spider blood are part of the immune system, and are used for healing wounds and stuff. There’s a chart comparing human blood cells to spiders’ here. That does not mean they’re interchangeable and Aunt May’s body would appreciate getting infused with them ….

But let’s pretend for a moment that Peter doesn’t have superpowers. His blood is just regular ol’ blood, whether the tests can tell or not.

We never do find out what blood type Peter is, or what blood type Aunt May is. In fact, at this point in the comics, we don’t know exactly how Aunt May is related to Peter. The fact that they share a last name suggests Uncle Ben was Peter’s dad’s brother, unless they adopted him and he took their last name. Assuming the former, Peter has no blood relation to his aunt, which means the likelihood of him being a compatible donor is the same as the likelihood he’s a compatible donor for Liz or Flash or the doctor.

Among Caucasian Americans, 37% have O+ blood, and 33% have A+. So if we’re randomly guessing, both Peter and May would probably belong to one of those. O+ can donate red blood cells to A+, but not the other way around.

Here’s a quick refresher on blood types: If you’re type A like I am, then your red blood cells have a protein on them called an “A antigen”, and your plasma has antibodies that attack red blood cells with the B antigen on them. If you’re type B, it’s the other way around. Type O red blood cells have neither antigen, and both antibodies in the plasma. And type AB red blood cells have both antigens, and neither antibody.

The antibodies are why you have to worry about who’s giving you blood. It’s also why the red blood cells have to be separated from the plasma before they can be donated. We’re often told O- is the “universal donor”, but if you just pumped a person’s O- blood straight into an A person, the A antibodies in the O plasma would attack the person’s own red blood cells (The B antibodies wouldn’t do anything, because a type A person already has them). AB plasma, on the other hand, can be given to anyone.

The +/- matters, too. That’s a separate antigen, known as Rh (D) (“Rhesus D”). If you’re a + you have it, and if you’re a – you don’t. Type – can be donated to type +, and + can be donated to a – exactly once (because after that, the body becomes primed to fight it).

If you botch a transfer with the wrong blood/plasma type, a patient can go into renal shock and die. So … don’t do that.

Wikimedia Commons, CC BY 3.0, InvictaHOG

In addition to ABO and Rh, there are 33 other recognized “blood group systems“, with more than 600 antigens that can be found (or not found) in blood. Some differences are restricted to certain ethnic groups. For example, people with African ancestry might have red blood cells that lack the Duffy antigen, which actually gives them resistance against malaria. I don’t think we have to worry about Aunt May not having that one.

So, let’s assume Aunt May’s body will accept Peter’s donation. I don’t know what the practice was in the 1960′s,2 but in this day in age, blood has to go through testing. You can’t just draw blood out of a person, hand them a sandwich, then pump it into a person with a compatible blood type – even if you’re 102% positive both people have the same blood type.

Maybe you’d resort to that if you were stranded in the middle of nowhere and the person was going to die ’cause there was no other blood lying around (I’m sure I’ve seen this on television or in a movie before), but not if you’re in a hospital. Even if the hospital was out of the blood they needed, they’d call around the city to get some that had already been vetted.

The other problem is the volume of blood needed. According to the Red Cross, the average red blood cell transfusion is 3 pints. But when donating blood, they only take 1 (or 0.5 L). The average adult body has 10 pints (or 5 L) of blood – being a pathetic teenager, Peter would probably have less.

But say he did. That means he’d be giving his aunt around 30% of his entire blood supply.

Losing that much blood would likely send him into hypovolemic shock.

But I mean, Peter was once willing to give up the life of his child to save his dying aunt, so he probably wouldn’t mind killing himself to do it.


1. A bit more detail: in a human’s closed circulatory system, red blood cells can’t leave the capillaries (ditto for certain proteins) so the “interstitial fluid” – i.e. the fluid in between tissues/organs – is kind of similar to blood plasma, but it’s distinctly different from blood. In the open circulatory system spiders and other creatures have, the hemolymph is all there is.

2. The first blood bank was established in Leningrad, in 1932. The American Red Cross blood program started in 1940, and in 1962 there were 4400 hospital blood banks in the US collecting 5-6 million units of blood per year.

The concept of blood typing and universal donors comes from circa 1910. Nowadays, blood is tested for many markers (in addition to ABO and Rh) that would make the blood unsuitable for transfusion, including Hepatitis B and C, HIV, syphilis, and Chagas disease. 

An earlier version of this post originally appeared on JD Voyek’s BadBackgroundScience blog, where she routinely examines the weird world of 1960’s Marvel science.

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