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  • They might look like rocks with tails, or messed-up giant bugs, but horseshoe crabs

  • are super old, super cool, and they deserve your respect.

  • They may have already saved your life.

  • First of all, they aren’t crabs. Theyre members of their very own family of arthropods

  • -- arthropods include insects, arachnids, and crustaceans -- known as Limulidae,

  • and there are only four species of them in the world.

  • Theyre more closely related to arachnids, like spiders and scorpions, than anything else,

  • but really, theyre their own deal.

  • Theyre also mega-ancient. The oldest horseshoe-crab fossil weve found is around 450 MILLION years old!

  • That means they have survived, virtually unchanged, for nearly half a billion years,

  • outliving pretty much everything else.

  • These guys are survivors.

  • So what makes them so tough? Well, part of it has to do with their amazing blood.

  • For one thing, it’s blue. Baby blue. Our blood is red because the substance it uses

  • to ferry oxygen around, called hemoglobin, contains iron. But horseshoe crabs use hemocyanin,

  • which is copper-based. So, just like iron turns red when it oxidizes, when copper meets oxygen,

  • it turns blue.

  • But that’s not even half of what makes horseshoe crab blood so cool.

  • So sea water is chock full of bacteria, and unlike mammals, horseshoe crabs don’t really

  • have an immune system -- no infection-fighting white blood cells at all. So if they get,

  • say, a crack in their shell, all that bacteria just gets into their bodies and could wreak

  • all kinds of havoc.

  • But what they do have is a glorious chemical -- found only in their blood cells -- that

  • binds to and inactivates unwanted bacteria, viruses, and fungi.

  • When the blood cells sense bad-guy invaders, they release a protein called coagulogen that

  • forms a gooey barrier around the infecting agents, preventing their spread.

  • That clot of gooieness also essentially creates a physical barrier, sealing up the wound and

  • preventing further infection. It’s an amazing internal defense mechanism.

  • Humans: we have no such ability. So for the past 50 years, weve been stealing it from

  • the horseshoe crabs.

  • Ever since American physician Fredrick Bang discovered the weird power of horseshoe crab

  • blood in the 1960s, these ancient sea creatures have played an essential, yet largely-unknown,

  • role in human medical treatment.

  • If you have ever received any kind of drug or vaccine injection, it’s because these crabs

  • made sure that injection was bacteria-free.

  • The whole thing starts when horseshoe crabs are collected from the wild, transported to

  • one of only five production labs in the world, and then rigged up for a blood drive.

  • Needles are inserted around the heart, and up to 30 percent of the animal’s blood is removed.

  • This stuff is liquid gold, and can go for $15,000 a liter.

  • From there, scientists extract the coagulogen from the blood cells, and use it to test solutions

  • that are used in injectable drugs and vaccines.

  • If the crab-blood extract finds unwanted bacteria in the solution, it immobilizes it in a gooey clot.

  • So if your sample doesn’t form any clots, you know that it’s bacteria-free

  • and safe for human use.

  • This simple procedure, called the LAL, or Limulus amebocyte lysate test, is nearly instantaneous,

  • and no other test works as well.

  • As for the crabs themselves, most seem to bounce back several days after being released

  • back into the wild, but some folks are concerned that the blood-letting weakens them more than we think.

  • So LAL manufacturers tend to only collect blood once a year, to ensure theyre not

  • double-dipping on the same crabs, and research is being done to come up with a synthetic

  • alternative so that we can eventually leave them alone.

  • Until then, next time you get a shot, give thanks to all those old horseshoe crabs who

  • made your good health -- and your sore arm -- possible.

  • Thanks for watching this SciShow Dose -- especially our Subbable subscribers. To learn how YOU

  • can help us keep sharing wonderful science like this, just go to Subbable.com. And don’t

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They might look like rocks with tails, or messed-up giant bugs, but horseshoe crabs

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