A pseudoscorpion from the United States
A pseudoscorpion, also known as a false scorpion or book scorpion, is an arachnid belonging to the order Pseudoscorpiones, also known as Pseudoscorpionida or Chelonethida.
Pseudoscorpions are generally beneficial to humans since they prey on clothes moth larvae, carpet beetle larvae, booklice, ants, mites, and small flies. They are tiny and inoffensive, and are rarely seen due to their size.
Pseudoscorpions are small arachnids with a flat, pear-shaped body and pincers that resemble those ofscorpions. They usually range from 2 to 8 millimetres (0.08 to 0.31 in) in length. The largest known species is Garypus titanius of Ascension Island at up to 12 mm (0.5 in)
The abdomen, known as the opisthosoma, is made up of twelve segments, each protected by plates (called tergites above andsternites below) made of chitin. The abdomen is short and rounded at the rear, rather than extending into a segmented tail and stinger like true scorpions (the fact that they look exactly like scorpions, aside from not having a stinger tail, is the source of the name "Pseudoscorpion"). The color of the body can be yellowish-tan to dark-brown, with the paired claws often a contrasting color. They may have two, four or no eyes.
Scientific classification :
A pseudoscorpion has eight legs with five to seven segments; the number of fused segments is used to distinguish families and genera. They have two very long pedipalps with palpal chelae (pincers) which strongly resemble the pincers found on a scorpion.
The pedipalps generally consist of an immobile "hand" and "finger", with a separate movable finger controlled by an adductor muscle. A venomgland and duct are usually located in the mobile finger; the venom is used to capture and immobilize the pseudoscorpion's prey. During digestion, pseudoscorpions pour a mildly corrosive fluid over the prey, then ingest the liquefied remains.
Pseudoscorpions spin silk from a gland in their jaws to make disk-shaped cocoons for mating, molting, or waiting out cold weather. However, they do not have book lungs as most of their closest relatives, the spiders, do. They breathe through spiracles, a trait they share with theinsects.
Some species have an elaborate mating dance, where the male pulls a female over a spermatophorepreviously laid upon a surface. In other species, the male also pushes the sperm into the female genitals using the forelegs. The female carries the fertilized eggs in a brood pouch attached to her abdomen, and the young ride on the mother for a short time after they hatch. Between 20 - 40 young are hatched in a single brood; there may be more than one brood per year. The young go through three molts over the course of several years before reaching adulthood. Many species molt in a small, silken igloo that protects them from enemies during this vulnerable period. After reaching adulthood, pseudoscorpions live two to three years. They are active in the warm months of the year, overwintering in silken cocoons when the weather grows cold. Smaller species live in debris and humus. Some species are arboreal, while others arephagophiles, eating parasites in an example of cleaning symbiosis. Some species are phoretic, others may sometimes be found feeding on mites under the wing covers of certain beetles.
Phoretic pseudoscorpion on a fly, Germany
There are more than 3,300 species of pseudoscorpions recorded in more than 430 genera, with more being discovered on a regular basis. They range worldwide, even in temperate to cold regions likeNorthern Ontario and above timberline in Wyoming's Rocky Mountains in the United States and theJenolan Caves of Australia, but have their most dense and diverse populations in the tropics and subtropics, where they spread even to island territories like the Canary Islands, where around 25endemic species have been found. Species have been found under tree bark, in leaf and pine litter, in soil, in tree hollows, under stones, in caves, at the seashore in the intertidal zone, and within fractured rocks.
Chelifer cancroides is the species most commonly found in homes, where they are often observed in rooms with dusty books. There the tiny animals (2.5–4.5 mm or 0.10–0.18 in) can find their food like booklice and house dust mites. They enter homes by "riding along" attached to insects (known asphoresy), the insects employed are necessarily larger than the pseudoscorpion, or they are brought in with firewood.
A book scorpion (Chelifer cancroides) on top of an open book
Here's Jon's information:
"They are surprisingly toxic, but only to tiny creatures as they are unable to pinch through human flesh or deliver any significant dose of venom. As it is their pincers that are armed with venom, they tend to react like mini, wee boxers when approached. I've found some to be even pugnacious and always ready for a fight, irregardless of any mismatch in weight classification. I have yet to find any way of keeping pseudoscorpions alive for more than several days, so I no longer try to keep them in captivity. It's just not fair to the wonderful little creatures. Domestically, I've observed that they usually irrupt from household hiding places whenever ant bait is set out to kill ants throughout a home. Perhaps there are ecological links between ants and pseudoscorpions.
I placed a small green fly, similar to a lacewing, in a jar with a pseudoscorpion once. When I saw that the fly was more than twice the size of the pseudoscorpion, I thought that maybe I should continue looking for more suitable prey. The pseudoscorpion approached the fly, however, and repeatedly jabbed at it it with its pincers. Within several minutes the fly was either paralysed or deceased and the pseudoscorpion was feasting upon it! Much to my dismay, however, the pseudoscorpion died two days later.
In a school in Toronto, Ontario, I set up a macro photography display and I used a mounted pseudoscorpion on a pin as my subject of focus. Each class in the school, with all the teachers and many parents, toured the exhibit after I presented a brief introduction and workshop on wildlife photography. 98% of all the participants in the tour lined up to view and practice focusing on the amazing little pseudoscorpion. Some of them, especially the kids of course, began looking for pseudoscorpions in their own homes. The venomous little wonder became a bit of a sensation in an inner city school that was very "challenging" to teach in.
I don't know if Australia has pseudoscorpions or not . . . if they exist there, I hope your school finds them plentiful and fascinating."
The oldest known fossil pseudoscorpion dates back 380 million years to the Devonian period. It has all of the traits of a modern pseudoscorpion, indicating that the order evolved very early in the history of land animals.
Historical references :
Pseudoscorpions were first described by Aristotle, who probably found them among scrolls in a library where they would have been feeding onbooklice. Robert Hooke referred to a "Land-Crab" in his 1665 work Micrographia. Another reference in the 1780s, when George Adams wrote of: "A lobster-insect, spied by some labouring men who were drinking their porter, and borne away by an ingenious gentleman, who brought it to my lodging." 
The numbers of recent genera and species are given in parentheses.
Chthoniidae (31, 605)
†Dracochelidae – one fossil species (Devonian)
Lechytiidae (1, 22)
Tridenchthoniidae (17, 68)
Feaellidae (1, 12)
Pseudogarypidae (2, 7)
Bochicidae 7 genera unknown number of species
Gymnobisiidae (4, 11)
Hyidae (3, 9)
Ideoroncidae (9, 53)
Neobisiidae (34, 498)
Parahyidae (1, 1)
Syarinidae (16, 93)
Vachoniidae 2 genera unknown number of species
Atemnidae (19, 172)
Cheliferidae (59, 292)
Chernetidae (112, 643)
Withiidae (34, 154)
Cheiridiidae (6, 69)
Sternophoridae (3, 20)
Garypidae (10, 74)
Geogarypidae (3, 61)
Larcidae (2, 13)
Pseudochiriididae (2, 12)
Menthidae (4, 8)
Olpiidae (53, 329)
Megathis Stecker, 1875 (nomen dubium, 2 species)
courtesy to : www.spiderzrule.com/pseudo
Here's another photo from a viewer -
A modern-day pseudoscorpion sitting on the head of a U.S. penny. This is actually an arachnid that mimics scorpions as a defense mechanism. They are only present when micro-organisms like lice and other bugs are present, or in very humid conditions.
Here's an interesting arachnid, called a Pseudoscorpion. It belongs to the same family as spiders, along with scorpions, mites and ticks. This photo was also sent in by Jon Triffo, from Saskatchewan in Canada. Here's Jon's information and his photo. Thanks for the great photo, Jon!!
Pseudoscorpions or "Book scorpions" are about 4mm long, flat-bodied arachnids with a short, usually oval abdomen. They have a pair of large pincer like claws (pedipalps) that project forward from the front of the body. There is no curved upward stinger from the rear tip of the abdomen as found in true scorpions. The body colour ranges from yellowish-tan to dark-brown, with the paired claws sometimes black. Some have 2 or 4 eyes while others have none. Legs are 5-segmented.
Wyochernes asiaticus female (around 2 mm long) with brood sac (photo by C. Ernst, reproduced here with permission)
Ten facts about Pseudoscorpions :
Yesterday I finally finished a draft of a manuscript about the natural history of a northern pseudoscorpion, and that task inspired me to write a ‘ten facts’ post about these truly astounding, tiny, Arachnids. Here goes!
1. Pseudoscorpions are commonly known as ‘false scorpions’ or ‘book scorpions’. The are their own Order within the Arachnida, and do resemble their cousins, especially the scorpions (hence their name!), except they don’t have a stinger on their back end. It’s suggested they were first described by Aristotle, perhaps as they were wandering among scrolls, hence the ‘book scorpion’ common name… In Micrographia, Hooke called these little critters ‘land-crabs’.
Hooke's 'land-crab' (pseudoscorpion) from Micrographia (1665)
2. In 2002 there were just over 3,000 known species of Pseudoscorpions. Mark Harvey considers the pseudoscorpions among a ‘neglected cousins’ within the Arachnida: they are seldom studied, and have received relatively little attention from biologists. Despite this ‘low diversity’ they are still more diverse than some other well-known animals: for example, the Carnivora order of mammals has fewer than 300 species!
3. This Order of Arachnids has an impressively long history, known from fossils going back to the Devonian, 380 million years ago! These arachnids have also been found in cretaceous amber,and it's clear that their body plan hasn't changed in quite some time!
4. Perhaps one reason these arachnids are poorly known is because they are easily missed: the largest pseudoscorpions don’t get over 10 mm in length, and most are much smaller than that. However, one cosmopolitan species often shows up in people’s homes, often in older houses and in damp areas of houses. That species is Chelifer cancroides, first described by Linnaeus in 1758. There’s a good overview about this species on the Encyclopedia of Life website. It’s an awfully nice-looking arachnid:
5. Although they are wingless, pseudoscorpions do get around. I’ve found them under rocks in high elevation areas well above the Arctic circle, and they are known pretty much around the globe. Their success at moving large distances is mostly attributed to their ability to ‘hitch-hike’ on other animals, a process known as phoresy. They can easily grab onto their host and hitch a ride. You can click here to learn more about phoresy in these arachnids, and Nicky Bay has a nice photo showing phoresy.
6. Although they are predators, pseudoscorpions don’t bite humans - they are tiny, and just don’t have the strength to pierce your skin. They tend to feed on tiny little invertebrates, including caterpillars, book lice, and other soft-bodied critters. Their venom glands, interestingly, are located on their giant, oversized pedipalps. They catch their prey, immobile their prey, and then macerate and suck out the insides of their prey, using their chelicerae.
7. I found found it’s often not particularly easy to find pseudoscorpions in nature, as their distributions tend to be quite clumped. Some good habitats include rotten logs, leaf-litter, and some species are known from organic debris on beaches. Sometimes get lucky and find a lot of specimens in a short period of time. This was the case when I was looking for Arctic pseudoscorpions in the Yukon Territory a few years ago. Here’s a video to illustrate the abundance, and to show how they move around.
8. Pseudoscorpions don’t have sex: sperm transfer is ‘indirect’. Males deposit a spermatophore (a ‘package of sperm’) on the substrate somewhere and the females must come in contact with that package in order for fertilization to occur. In some species, males will do ‘dances’ with females and help her find the spermatophore. Weygoldt’s book describes the full suite of these behaviours. However, in some species, males have never been found! Nelson, for example, collected hundreds of specimens of Microbisium confusum without finding a single male. It’s therefore assumed some species are parthenogenetic. Once eggs are laid (kept within brood sacs of the female), there are three larval stages: protonymphs, deutonymphs, and tritonymphs.
9. The natural history of most pseudoscorpions are largely unknown, but there are some remarkable exceptions including the work by Zeh & Zeh on Cordylochernes scorpioides, which catches a ride on harlequin beetles, and in which the males will defend the beetle’s abdomens as good sites for intercepting (and inseminating) dispersing females. There’s also a paper that described matriphagy in one species. The authors write: “...the mother went out of the nest and passively awaited the protonymphs’ attack, not reacting to the capture nor to the nymphs feeding on her body”. Yuck.
Pseudoscorpions can easily fit in the palm of your hand!
10. Pseudoscorpions can be tricky to identify, but to become familiar with the group, you should check out Mark Harvey’s websites. If you live in northern North America, you can refer to this photographic key. Otherwise, Muchmore’s key in Dindal’s soil biology guide is probably the best resource.
Pseudoscorpion Zoology (Ireland)
Some Videos :
Further Reading :
by Peter Weygoldt