Tiny Hitchers

Among the strangest creatures you are likely to encounter in Missouri are tiny arachnids called pseudoscorpions. (Spiders, scorpions, mites, and ticks also belong to the class Arachnida.) They look like miniature scorpions, but without tails. Most species are 5 millimeters in length or less, but they can travel far and wide. They are common under bark on trees and logs, in leaf litter and humus, in caves, and in the nests of birds and small mammals. Sometimes they even show up indoors. How they get there is fascinating.

Pseudoscorpions don’t have wings, but they take advantage of beetles and other insects that do by hitching rides. Using another animal for transportation is called phoresy, a fancy scientific term for hitchhiking. A pseudoscorpion uses its chelae, or pincerlike claws, to grab onto a leg or other body part of an insect. They have quite a grip and are not easily dislodged as the insect walks and flies. Once the little arachnid arrives at a destination it likes, it releases its hold and goes on its way.

Those claws also have another trick: they contain venom glands that help subdue prey. They are harmless to humans, yet eat many pests, such as the larvae of clothes moths and carpet beetles, plus ants, dust mites, barklice, springtails, small flies, and booklice, so they are considered beneficial. They also have jaws (chelicerae) that do more than just chew up a meal. Many species of pseudoscorpions have silk glands in their jaws. They use that silk to construct sack-like shelters in which to molt, hide from bad weather and protect their young.

Male pseudoscorpions deposit their genetic material, or spermatophore, on a stalk on the ground, tree bark, or other surface. Most of time, the female is present and determines whether to accept the material. In the more advanced families of pseudoscorpions, the male may perform an elaborate dance and lead his prospective mate to his offering.

The female produces a small number of embryos that emerge into a brood sac beneath her abdomen. The young hatch and stay with their mother for a short time before dispersing. Young pseudoscorpions grow and molt and progress from protonymph, to deutonymph, to tritonymph, and then, finally, they become an adult pseudoscorpion.

A conservative estimate is that there are probably more than 20 species of pseudoscorpions in Missouri. Many are very particular in their habitat requirements, and a few are found only in caves (some species are restricted to only one particular cave each). This makes them highly vulnerable to extirpation, or loss. No pseudoscorpion is currently on the Missouri state list of threatened and endangered species.

The species you are most likely to see is Chelifer cancroides, as it has found its way to virtually all corners of the world, hitching rides not only on insects, but global commerce, too. Many more species undoubtedly remain undiscovered, or at least unknown in the Show-Me State. Maybe you will be the person to find one.