Palpigradi are commonly called micro whip scorpions. Fewer than 100 species are known representing two families – the Eukoeneniidae & Prokoeniidae. These are tiny arachnids, no more than 3 mm in length (some as small as 0.65 mm). Palpigrades live under stones, rocks, and in caves where the humidity is high – one species lives in catacombs of St. Stephen’s Cathedral in Vienna! They have no eyes and no respiratory organs. Gas exchange most likely occurs through their thin cuticle via diffusion, although there are “sacs” or lobes on the underside of the body that may be involved in respiration. As they move, palpigrades hold their first legs aloft and use them to sense the environment. However, they use their longer pedipalps like legs for locomotion – this is very unusual for arachnids. The long, whip-like flagellum covered with bristles is distinctive but its function is unknown.
Most palpigrades are predators although recent research demonstrated that cave species seem to eat cyanobacteria. Females are larger than males. Courtship, mating, and reproduction in these tiny arachnids is largely unknown. Most likely males produce a spematophore and females produce only 1 – 3 eggs.