( Latin: Order Psocoptera) 

The names booklice and dust lice are used somewhat indiscriminately. Booklice are light-shy insects that thrive best when the humidity is over 75%. There are several species. Some, such as Liposcelis divinatorius, have no wings and cannot fly, while others, the so-called winged booklice, e.g. Atropus pulsatorius, have small but non-functional wings.

Booklice run about actively when disturbed, with characteristic jerky movements, and they can also make small, rather clumsy, jumps.

As the name implies, booklice are found between sheets of paper in libraries and archives, and also behind loose wallpaper and in herbaria. They do not eat the paper itself, although they may feed on the glue in glazed paper, but they subsist primarily on the moulds growing on the paper. In- deed, the presence of numerous booklice is a sign that the paper is being kept too damp.

Some booklice can produce a ticking sound by striking the abdomen against the substrate (p. 214).

In the present context, the term bookworm refers to the larvae of certain wood-boring beetles which feed on paper (p. 122). These larvae require a high humidity and nowadays they rarely attack books. They only occur in books which stand undisturbed for years in cellars or lofts.

Beetles and other insects with wood-boring larvae may, when they make their way out of timber, gnaw holes in paper that is nearby, as for example wallpaper.

Drugstore beetles, tobacco beetles, spider beetles, dermestid beetles and moth larvae, to name only a few, will gnaw through paper, cardboard and plastic packing, and holes in the packaging will often be the first sign that the goods contain live animals.

Mice and rats sometimes cause a great deal of damage to paper and plastic. They can easily gnaw through packaging made of these materials and often use the fragments as nest material.

The activities of these rodents can be recognised by the tooth marks (p. 84), which can always be identified, even in the thinnest sheet of newspaper. They might be confused with holes torn by a cat or a marten, but here one would normally see distinct claw marks.

These insects are not related to the true lice. They prefer damp places, such as cellars, damp outside walls, or outhouses, and they may be found in new houses before the walls are dry. They cannot tolerate dryness.
A female booklouse can lay a couple of hundred eggs, and under favourable conditions development to sexual maturity takes about a month, so it is not surprising that booklice often occur in very large numbers. In kitchens and stores they mainly attack flour, cereals and other goods containing starch, and they have a fantastic ability to get into packets that are not tightly sealed. They are in no way dangerous to health, but may cause commercial losses if they become established in grocery stores.