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Book-lice and Their Allies — Part 1

(Order Corrodentia.)

The curious little wingless insects known as book-lice, which are found frequently in numbers among old, dusty books in damp places, and the interesting little bark-inhabiting creatures known as Psocids are structurally so different from all other insects that they have been brought together in the order Corrodentia.

Those which are winged have four wings with prominent veins but very few cross veins. The fore wings are larger than the hind wings, and both are held in a roof-shaped manner over the back when not in use. The mouth-parts are formed for biting, and all of these insects have very incomplete metamorphoses.

The true Psocidae (I regret that there is no popular name for these insects, for they are very interesting, and always attract attention when seen) live together in curious little colonies on the bark of trees, especially old trees covered with a growth of lichens, or even upon the surface of old fence boards. They possess the power of spinning a certain amount of silk, and each colony is generally covered with a delicate silken web. The eggs are laid together in clusters, and the development of individuals is rather rapid.

Psocus venosus is a common form in most parts of the country, and its habits have been described by Hubbard, who has studied it in its southern range upon the trunks of orange trees in Florida. It is small and smoky-brown in color, and is seen upon the trunks of trees in flocks numbering from a dozen to forty or fifty individuals. They feed in companies and browse upon the lichens, which they cleanly remove from the bark, leaving a clear space behind them. The colonies consist of one or more families, and include individuals of all ages, the wingless young herding with the adult insects. The adults, although winged, do not readily take flight. When alarmed the whole troop huddles together apparently for mutual protection like sheep, but when seized with a sudden panic they scatter in every direction and run rapidly over the bark, their color harmonizing so closely with that of the bark that they are not easily distinguished. Soon after they reassemble and begin to eat the lichens.

The eggs are oval, glistening white, and are laid upon the bark in batches of fifteen to thirty, deposited on end in several rows, and each cluster is protected by an oval, convex shield of gnawed-up wood which adheres closely to the eggs. The females brood over the eggs, see that they are not disturbed, and, when they hatch, lead the young ones forth to pasture.

This insect is fond of shade and moisture, and is most often seen in densely shaded groves and old gardens. The adults, according to Hubbard, hibernate, and begin breeding early in the spring.

Hubbard has also studied another species, Psocus citricola, which is probably a Southern form. With this species the eggs are laid in hollows upon orange leaves in little clusters covered with a shield of black excrementitious matter. Over this is stretched a slight silken web. The embryo is plainly seen through the shell, and when ready to hatch air bubbles are seen which pass in rapid succession between the mouth-parts and collect in a larger bubble within the head. From time to time this larger bubble passes down into the body cavity. The head swells-elongates-distends the eggshell at the end until it bursts, and then the young insect protrudes its body. Air continues to pass through the neck into the abdomen, which becomes greatly distended and elongated, and this distention causes, probably, the bursting of the first larval skin. The process of hatching occupies several days.

This species lives upon the leaves of plants associated in small flocks, and passes the greater part of its life hiding under the canopies of webs spun over the egg clusters. Here the mother awaits the appearance of her brood, and here the young insects cluster, sallying forth from time to time with the mother in search of food.

The book-lice belong to another family, the Atropidae. They are very small and some of them have been supposed to make a ticking noise which in olden times caused them to be known as "death watches."

These little insects are widely distributed, and are commonly seen on library shelves and in old records in closets. They are omnivorous, feeding on any animal or vegetable matter, and are especially fond of the starch paste used in book bindings or under wall paper. They feed on flour and meal, and are often found in natural history collections, living on the specimens. They are sometimes found in straw beds and in the straw coverings of wine bottles. A case has been recorded in Insect Life in which they bred so extensively in a mattress of hair and corn husks that "a pin point could not have been put down without touching one or more of the bugs." They swarmed over the sheets and the walls of the room; bureau draws were swarming with them, and the mattress no doubt contained them by the millions.