Be afraid. A new terror is descending on your home and it lurks in your . . . er . . . bookcase? The terror in question is a fearsome little creature called Chelifer cancroides, one of the most common species of pseudoscorpion (there are actually about 2,000 species in the world). Ok, they are not scorpions, hence the pseudo- in front of their name, but they certainly look like the real thing. Their front legs extend into pincher-like claws that give the small arachnid a menacing appearance. However, these little critters do not pose any danger to you, the human, but be afraid if you are a book louse!
Pseudoscorpions like to hang out in old books, but they are not seeking knowledge. Rather, these little critters are predators who hunt tiny arthropods, especially booklice. The battle of the pseudoscorpion and the book louse is a tale as old as time. Book lice find the starch-based glue used in book binding particularly tasty and set up their homes in old books slowly destroying the binding holding the tomes together. Pseudoscorpions keep these miniscule book lice at bay by hunting them on the battle ground of your book shelf. The pseudoscorpion immobilizes the louse with poison found in glands on their pedipalps, or front pinchers. They tear the louse open using their chelicerae, or mouth parts, and suck out the unfortunate and still alive louse’s bodily fluids.
Gruesome, no? And it is happening in your library. Barbaric.
Although they live in a wide range of habitats, don’t be surprised if you never see a pseudoscorpion. Their teardrop-shaped bodies are only 3–4 millimeters in length—that is about the thickness of three or four stacked pennies. Like other arachnids, the pseudoscorpion has four pair of legs, with the front pair forming the pinchers. For the insect world, pseudoscorpions are long in the tooth, with males living up to four years. These little arachnids also are quite adventurous, hitching a ride with a flying insect, like a fly, to travel to new hunting grounds.
Pseudoscorpions are far from endangered, but their numbers are thinning thanks to changes in the book binding process. Because these little critters do not harm people and offer a natural pest-control service, put the pesticides away. If you are fortunate enough to pull a book from the shelf and find a pseudoscorpion, say thank you for a job well done.