Sometimes I am asked why I study animals so unimportant to human life and economy as pseudoscorpions. There is one simple answer: every aspect of nature that interests the human mind is worthy of study whether or not it is of direct importance to man.
Peter Weygoldt, The Biology of Pseudoscorpions
Pseudoscorpions' large claws (pedipalps) make them look like scorpions, but they lack the true scorpions' stings and are usually much smaller than the latter. The specimen pictured above, about 3 mm long, was one of the largest I have seen. Some species of pseudoscorpions do have poison glands, but these open near the tips of their pedipalps1.
Pseudoscorpions are quite common in soil, but because most species are only a few millimeters in length, they usually escape attention. The only time I come across them is when I am sorting through forest soil samples for tiny snails.
Pseudoscorpions are predators that feed on other small arthropods. They also have a peculiar behavior of attaching themselves to the bodies of larger arthropods, for example, flies, and allowing themselves to be transported in this fashion. This is known as phoresy. Phoresy presumably helps the pseudoscorpions to become dispersed over large areas1.
Michigan Entomological Society's Entomology Notes #16: Pseudoscorpions.
Fossil pseudoscorpions in Baltic amber.
1. Peter Weygoldt. 1969. The Biology of Pseudoscorpions. Harvard University Press.