There’s something special about the smell of old books. The warm musty scent of yellowed pages sparks the image of ancient knowledge and timeless tales. Libraries aisles and basements alike can be filled with this calming, vaguely vanilla fragrance when filled with antique text. It’s almost as if the words themselves are exuding the aroma to coax the reader into the mystical worlds among their pages.
Of course, the source of this odor is not some magic incantation, but instead simple science. As books break down, they release volatile, or airborne, chemicals. These chemicals are then inhaled through our noses, interact with receptors, and are interpreted by our brain as a slew of scents. The breakdown of pages, covers, and starch-based bindings release variable chemicals, and in turn are interpreted as variable smells. In one study, researchers established “The Historic Book Odor Wheel,” classifying book smells into 8 categories, which are further divided into specific smells and their chemical sources. Using this information, historians can tell the age of a book, where the book was made, and the level of deterioration.
However, humans are not the only ones attracted to an old book’s smell. Psocids, commonly referred to as booklice (Order Psocodea), are small insects (0.6-25mm) that inhabit a variety of habitats, including old books. Drawn in by the delicious aroma of decaying pages, psocids feed on microscopic fungi that grow on old books, as well as the starchy paste that binds the pages together.
When psocids first hatch (or born, as some species do perform live birth), they resemble their adult forms with big heads, wide abdomens, and long antennae. As they develop, they molt and grow until they reach adulthood, where they are finally ready to start their family.
On top of the pages, the male psocids begin courting the female by dancing in circles around her and vibrating his antennae (some species vibrate their wings as well, although most indoor species are wingless). If she is impressed with his dance, the two will mate. If she is not, she may be unimpressed, busy reading, or possibly parthenogenic. Parthenogenic females are organisms that can produce an embryo asexually, or from an unfertilized egg. Parthenogenesis is common among many psocid species, sometimes leading to the formation of new races and species of psocids.
No matter the means, the female lays a couple dozen eggs coated in a protective webbing or crust, depending on the species (this is not the case for the few species that give live birth). The eggs then hatch, thus restarting the psocid’s literature-based lifecycle.
Psocids are short-lived, with a typical lifespan lasting less than a month. Although they typically do not damage books, in large enough numbers they can be a nuisance. They’re also not alone among the pages. Dust mites also live within these texts, eating whatever organic material they can find. Unlike psocids, dust mites are not insects but arachnids, closely related to spiders. As they develop, they go from having six to eight legs, and females can live up to 80 days.
Neither dust mites nor psocids directly affect humans, however, people can be allergic to their remains or excrement. With this, many people are not particularly fond of their books being inhabited by these small critters. Minimizing the humidity books are exposed to can help limit these creatures’ populations, however, it is unlikely this alone will get rid of them all. Pesticides can also be used, but sometimes it’s best to let nature work itself out. After all, books can be dangerous places for psocids and dust mites. Among the ancient pages of these books lurks a voracious, tiny predator: the pseudoscorpion.
Pseudoscorpions (literally meaning “fake scorpion”) are small arachnids that inhabit a range of different habitats, including old books. Pseudoscorpions can live up to four years, and resemble a small, fat scorpion, minus the tail. Their two front pinchers, referred to as pedipalps, may seem scary, but pseudoscorpions are completely harmless. Unless, of course, you are a psocid or dust mite.
Pseudoscorpions vary in their hunting strategies, with some individuals actively stalking their prey while others wait in ambush. Having poor eyesight, pseudoscorpions rely on sensitive hairs, or sensilla, to feel for prey. Once prey is sensed, they grasp the individual, injecting it with venom from glands on their pedipalps. This venom paralyzes their prey, on which the pseudoscorpion bites and fills with their saliva. The pseudoscorpion’s saliva breaks down the insides of its prey, allowing the pseudoscorpion to drink it like a bug smoothie. Full, but not satisfied, the pseudoscorpion discards its victim and begins hunting again.
Much like psocids, male pseudoscorpions too perform dances for their mates, often involving rapid body movements so the female can sense his “good vibrations.” If the female is interested, the male places a sack of his sperm onto the ground and guides the female to pick it up. Following copulation, the female carries the fertilized eggs around with her until they hatch. Once hatched, the young pseudoscorpions often will hang around with their mother, sometimes hitching rides on her back. After a few days, the young pseudoscorpions will leave their mother’s side, venturing out to prowl the pages alone.
So next time you see (or smell) an old, mysterious book, remember that no matter the genre, there are interesting, romantic, and sometimes dramatic lives being led upon those yellowed pages.
[Note: It is important to reiterate that although these creatures (psocids, dust mites, pseudoscorpions) appear alarming, none of them are outright harmful to books, or to humans. The point of this article is not to scare you or gross you out, but instead showcase the intricate, amazing lives led in even the most inconspicuous places. Spraying down books with pesticide will likely do more harm than good and is often unnecessary. If you are worried about your books, I once again encourage you to keep them in a cool, dry location to minimize the number of inhabitants.]
