Pseudoscorpions are a group of generally small arachnids (adults typically 0.5 to 5 mm long) that are not often encountered by most people. For those alert to tiny creatures, however, the most frequently encountered species is probably the House Pseudoscorpion (Chelifer cancroides). This species has a cosmopolitan distribution and often occurs in human dwellings or other buildings.
House Pseudoscorpions are 3 to 4 mm in length and have a rich mahogany color. The four pairs of legs increase sequentially in length from the 1st to the 4th pair. There is a single eye on each side of the cephalothorax (head plus thorax) and a 12-segmented abdomen (although only ten segments are easily visible). Excluding appendages, the body resembles a teardrop. The pedipalps, located in front of the first pair of legs, are more than twice as long as the legs. When extended, crab-like, they measure 7 to 9 mm across.
Mature male House Pseudoscorpions establish a mating territory 1 to 2 cm in size. They rub their ventral (lower) surface on the center of this territory, possibly depositing pheromones. When a female enters this area, the male begins a mating dance by rapidly vibrating his body and displaying his pedipalps. He deposits a spermatophore (a sperm packet) on the substrate, moves backwards over it, and guides the female on top of it. The entire mating process takes from 10 minutes to 1 hour.
The female produces 20 to 40 eggs which she carries beneath her abdomen. After the young House Pseudoscorpions (which resemble miniature adults) emerge, they stay with the female for several days, sometimes riding on her back. The entire brood then disperses. This entire process, from egg deposition to brood dispersal, can take 3 weeks.
The young House Pseudoscorpions molt three times before adulthood. The developmental period is temperature-dependent, but ranges from around 10 to 24 months. Adults do not molt and can live for 3 or 4 years.
Pseudoscorpions pose no danger to humans, but they may pose a substantial threat to even tinier arthropods that may be living in their vicinity. Unlike the superficially similar true scorpions, pseudoscorpions lack a stinger in the tail, but instead possess poison glands in the pedipalps with which they imobilize prey (e.g., mites). Once captured, their victims are torn open with the chelicerae and the body fluids are sucked out. Like some other pseudoscorpions, House Pseudoscorpions may disperse by hitching a ride with a larger arthropod (often a flying insect), grabbing onto a host with their pedipalps. House Pseudoscorpions may be found tagging along with house flies.
(Brusca and Brusca 2003; Jacobs 2006)
- Jacobs, S.B. 2006. Pseudoscorpions: House Pseudoscorpion (Chelifer cancroides). Entomological Notes, Pennsylvania State University Cooperative Extension, University Park, Pennsylvania. http://ento.psu.edu/extension/factsheets/pseudoscorpions.
- Brusca, R.C. and G.J. Brusca. 2003. Invertebrates, 2nd edition. Sinauer, Sunderland, Massachusetts.
- Levi, H.W. 1948. Notes on the life history of the pseudoscorpion Chelifer cancroides (Linn.) (Chelonethida). Transactions of the American Microscopical Society 67(3): 290-298.
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