What are pseudoscorpions?

Pseudoscorpions are small arachnids that bear a pair of chelate pedipalps, a pair of two-segmented chelicerae, four pairs of legs, and an ovate abdomen. They superficially resemble small scorpions but they lack the elongate tail (metasoma) and sting.

They are considered to be most similar to sun-spiders (Solifugae) as both groups share numerous features in common, such as an elongated femur-like patella on all legs, coxae that meet in the mid-line, two-segmented chelicerae, paired tracheal stigmata opening on opisthosomal sclerites 3 and 4, and the apotele of each leg with a soft empodium or pulvillus (termed an arolium in pseudoscorpions). These two orders represent the only members of the Haplocnemata.

Pseudoscorpions transfer sperm in packages attached to a spermatophore, which is produced from the male’s gonopore and attached to the substrate. Males of most families that have been studied (Chthoniidae, Tridenchthoniidae, Pseudogarypidae, Neobisiidae, Garypidae, Larcidae, Geogarypidae, Olpiidae and Cheiridiidae) simply deposit a spermatophore without any courtship or even in the presence of a female. The females somehow find the spermatophore and draw the sperm packet into the gonopore. Males of Serianus (Garypinidae) deposit a spermatophore in the presence of a female, but there is no physical contact between the pair. Members of the Cheliferoidea (Atemnidae, Cheliferidae, Chernetidae and Withiidae) perform an elaborate mating dance in which males actively court females, touching and posturing the females, culminating in grasping the female with his pedipalps, depositing a spermatophore on the substrate. He then assists the female to move over the spermatophore, and she then draws the sperm packet into her gonopore.

The eggs mature internally and the embryos are deposited into a brood-sac attached to the gonopore. The embryos mature until the protonymphs emerge from the brood-sac. They remain with the female for a short time and eventually disperse for a solitary existence.

There are four post-embryonic stages, protonymph, deutonymph, tritonymph and adult. The nymphal stages are generally free-living although the protonymphs of some species are immobile. The adults do not moult any further.

Many pseudoscorpions build a small silken chamber in which to moult, develop their brood-sac, or shelter from hazardous environmental conditions. The silk discharges from a tube (the galea) situated at the end of the movable cheliceral finger. The silk glands are situated in the cephalothorax.

All pseudoscorpions of the suborder Iocheirata possess venom glands within one or both of their chelal fingers. The active components of the venom are unknown.

Many pseudoscorpions have been found association with other animals. Some are obligate commensals spending their entire life cycle in the nests or fur of mammals (e.g. many species of Lasiochernes and Megachernes). Others form associations with flying insects, attaching themselves to legs, other body parts or, sometimes, under the elytra of beetles.