Booklice’s tiny pincer nemesis hides in homes unnoticed
Pseudoscorpions are flat, pear-shaped arachnids with scorpion-like pedipalp pincers but no stinging tail. Usually 2–8 mm long—Garypus titanius of Ascension Island reaches 12 mm—they prey on clothes-moth and carpet-beetle larvae, booklice, ants, mites, and small flies, quietly helping households.
Pseudoscorpions, also called false scorpions or book scorpions, form the arachnid order Pseudoscorpiones. They have flat, pear-shaped bodies and a pair of long pedipalps ending in pincers that look just like a scorpion's. Most measure 2 to 8 mm, averaging about 3 mm; the giant of the group, Garypus titanius from Ascension Island, reaches 12 mm. Bodies range from yellowish tan to dark brown, often with contrasting claws, and they may have two eyes, four or none.
Each of the eight legs has five to seven segments, and the number of fused segments helps separate families and genera. Each pincer has a fixed hand and a movable finger worked by a muscle. In the Iocheirata, which include most species, a venom gland in the movable finger subdues prey; the animal then coats its meal in a mildly corrosive fluid and swallows the liquefied result. None of this is medically significant to people. The abdomen has 12 segments shielded by hardened plates and ends in a rounded rear rather than the segmented tail and sting of true scorpions. They breathe only through tracheae opening at two pairs of spiracles, not through book lungs, and they spin silk from a gland in the jaws to build disc-shaped cocoons for mating, moulting or sitting out the cold.
Mating is indirect. The male fixes a sperm packet to the ground and the female picks it up; in the Cheliferoidea an elaborate dance ends with the male steering her over it. Species with a sperm-storing organ can delay fertilisation for a long time. The female carries her eggs in a brood pouch, and a brood yields 2 to 50 young, sometimes several times a year. The young pass through three nymph stages; embryos and first-stage nymphs are fed a milk made by the mother's ovary, and many moult inside small silk igloos.
They are common but so small that they go unnoticed or are mistaken for ticks or tiny spiders. Their diet makes them useful house guests, since they devour the grubs of fabric pests along with booklice, ants, mites and tiny flies, and they often hitch rides on other animals, a habit called phoresis.
Source: Pseudoscorpion
