Book scorpions are the best/worst thing to happen to books, because book scorpions! But also book scorpions…

Properly known as pseudoscorpions, these tiny, tiny creatures have a fondness for old books, because old books also happen to contain delicious booklice and dust mites. And they’re really not book scorpions… at all because they can’t hurt us, and they’ve basically been performing a free pest control service since humans started stacking excessive numbers of dusty, bound-together piles of paper along our walls and nightstands. This arrangement works because old book-makers used to bind books using a starch-based glue that booklice and dust mites love, so without a healthy population of book scorpions patrolling your collection, those gross parasites are probably having a horrible, silent field-day chewing them all apart.

Of the 3,300 or so known species of pseudoscorpion, the most commonly encountered is Chelifer cancroides. Found all over the world and growing to no more than 4 millimetres in length, C. cancroides looks just like a scorpion, thanks to its enormous pair of long, pincer-like claws called pedipalps. C. cancroides's pedipalps are twice as long as its legs, but it still manages to carry them right up in front of its head or out beside it like a nice warm thin, spiky and uncomfortable hug.

When they’re not patrolling old books or supporting oversized appendages with their tiny heads, book scorpions are having weird sex. Weird sex that involves a lot of dancing and rubbing. The process starts with a male cordoning off a ‘mating territory’ that’s around 1-2 centimetres in size. They do this by rubbing their abdomens in the centre of this space, which presumably deposits some kind of pheromone. Once a female has been lured into the arena, the male will begin his glorious courtship dance, vibrating his body rapidly and showing off his pedipalps by waving them around in what we can only assume to be a seductive manner, all in an effort to prove that he is worthy and capable of creating strong and healthy offspring with this fine lady in front of him. And oh great, she's interested! Time to commence the forepl--

Nope. Nope. These are arachnids. And what's the arachnid version of foreplay for our lucky male book scorpion?

He dumps a sac full of sperm on the ground.

And it gets worse, because then he pushes the female down into his sac full of sperm on the ground.

This whole process can take anywhere from 10 minutes to a whole hour. The sac full of sperm will be taken in by the female's genital orifice, and she’ll end up producing 20 to 40 eggs, which she’ll carry around in her abdomen, even after they’ve hatched. The larvae will remain inside for for some time, attached to her genital orifice and feeding on a milk-like substance produced by her ovaries until she’s become so emaciated, they just have to leave. And just like larger, actual scorpions, book scorpion mothers are cool with carrying their offspring on their backs until they’re old enough to disperse and conduct their own very important book patrols.

Also, guess what the respiratory organs of book scorpions are called. They’re called book lungs. And not because they belong to book scorpions. Real scorpions and spiders have them too. They're called book lungs because they're built with alternating stacks of air pockets and layers of tissue filled with insect blood - hemolymph - that look just like the warped pages of an old book.

Here's a book scorpion being adorable to ridiculous music:

Thanks to Alissa Walker at SPLOID for the tip.

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