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    When humans head out into the desert we pack as much food and water as we can carry, for obvious reasons.  Camels also stock up on rations.  They pack their humps full of fat so they don't go hungry.  And since they can go up to two weeks in the hot desert with no water at all, you might think they have a nifty place inside them where they stash liquid too.  Kind of like a, uh,  Camelbak.  But they actually don't, they're just really good at keeping the water they already have, surviving with very little, and then near instantly filling back up when they get the chance.  And they have some pretty cool evolutionary tweaks, especially to their blood, that help them do that.  If you watch a camel drink after a long spell without water, it's easy to see where people might have gotten the idea that they store the stuff somewhere.  These animals can down more than a hundred liters of water in a few minutes, but they aren't actually overhydrating.  They're just replacing what they've lost.  Still, that kind of quick drinking would kill most other mammals, and that's because it would rapidly dilute their blood.  The concentration of salt and other molecules inside their red blood cells would suddenly be a lot higher than in the serum around them, so water would go rushing into the cells to equal things out, which would cause those cells to explode.  Luckily for camels, they can hold a large amount of liquid in their first stomach, or rumen.  It let's all that water out into the blood over several hours, giving their bodies more time to safely shift things around.  

   The red blood cells are also practically unbreakable.  They can swell to more than twice their regular size without bursting.  And those same red blood cells also help them survive too little water.  Camels can lose nearly a third of their body weight in water, which is two to three times more than most other mammals.  That's in part because camel blood cells are small and oval-shaped, which helps them flow through tight spaces.  You see, when you're dehydrated, your blood volume decreases, so to keep your blood pressure steady, your blood vessels get narrower, which is exactly when small oval cells would come in handy.  Camel blood also has unusual fluid properties.  Normally, dehydrated blood gets thick, and blood cells start to stick together.  But camel blood doesn't get thick or clumpy when it's concentrated or moving slowly.  In fact, it doesn't really get viscous at all, even when it's cool.  Which comes in handy for one of their major water conservation strategies: not sweating.

   Many mammals, including us, sweat to cool off, but that uses a lot of water.  So camels basically don't sweat, though their regular body temperature is around thirty-seven degrees celsius, they won't start sweating until it hits forty-two, which helps them conserve water and energy.  Instead, they absorb heat during the day, and cool off at night when their environment is chilly anyway.  

   And camels have a bunch of other tricks for conserving water, like their kidneys and large intestine are super water efficient so they lose very little through their excretions.  In fact, if camels have a super power, it's not their ability to survive dehydration or near-instant rehydration, it's their ability to hold onto the water they already have.  

   Still, what they don't have is a bladder full of extra water tucked away somewhere they can slowly sip from as they walk around the desert.  They just have amazing blood.

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