Pseudoscorpions originated in pre-Devonian times, more than 400 million years ago, and are one of the oldest living animal groups, having diverged into more than 3 400 species in 26 families. Because of their small size and lack of medical and agricultural importance, pseudoscorpions have been studied by only a small group of scientists, mostly taxonomists. Only recently have these arthropods begun to gain the interest of a wider audience.
The unusual appearance and secretive nature of pseudoscorpions was recorded as far back as the days of Aristotle. However, even Linnaeus failed to clearly define them, grouping the first two described species (Acarus crancroides and A. scorpioides) with mites and harvestmen. Superficially, pseudoscorpions resemble true scorpions, but lack the elongated tail and sting. They do, however, share the six-segmented pedipalps, with the tibia and tarsus modified into a chela (claw) with a movable ‘finger’. The chelae house some of the pseudoscorpion’s most sensitive sensory structures and are used primarily for environmental awareness and subduing prey. Members of the suborder Iocheirata possess venom teeth on either one or both of the chelal ‘fingers’. The carapace (upper shell) may house either one or two pairs of eyes on the front, although some cave-dwelling species either lack eyes completely or have them in a reduced form.
All pseudoscorpions are predatory and the study of fossilised specimens from 50-million-year-old Baltic, and younger Dominican and Mexican amber, show that this has been the case for millions of years. Although they range from less than 1 mm to just over 10 mm most are less than 5 mm in length.
Pseudoscorpions occur in almost every part of the world, although most species occur in the tropics and subtropics. Their unique morphology makes these secretive creatures a very important predatory component of many terrestrial habitats, where they may be found in humid soil, leaf litter and piles of compost, under stones, bark and logs, as well as in harsh environments such as intertidal zones. Although most species are ground-dwellers, many arboreal representatives are also present. Chelifer cancroides, a cosmopolitan species, is often found in man-made structures.
Some species occupy very specific niches, such as caves. ‘Insectloving’ species such as Ellingsenius sculpturatus is strictly associated with bees, and Marachernes bellus is associated with ants. Both these species live with their hosts and feed on parasites in the hives and nests. Many species have also formed commensal relationships with a myriad of birds and mammals.
One of the best documented facts of pseudoscorpions is their association with flying insects. The pseudoscorpion attaches itself to a host insect by grasping it with its chelae, and then travels along with its host to a new location where it then detaches itself. The exact reasons for this behaviour are still being debated, although the most popular theory is that it is a method of dispersal.
Pseudoscorpions generally have a solitary lifestyle and avoid social interaction. There is often aggressive behaviour both within and between species. However, there are a few social species that go beyond merely aggregating in large numbers. Paratemnoides elongatus, for example, exhibits one of the highest levels of social organisation currently known among pseudoscorpions, with co-operative spinning by immatures as well as simultaneous moulting. Adults and tritonymphs (the final juvenile stage) also engage in co-operative predation, which enables them to capture prey many times their own size.
Another observed behaviour of particular interest, is matriphagy in Paratemnoides nidificator. The females, which are responsible for all brood care, allow nymphs to attack and feed on them during periods of food deprivation. It is hypothesised that this behaviour leads to a decrease in cannibalism among the nymphs themselves, as well as contributing towards the evolution of social behaviour in the species.
What do we know of pseudoscorpions in South Africa? With 152 described species in 17 families, and 70% of these species being endemic to the country, South Africa has the eighth largest pseudoscorpion diversity on the planet. Not bad, considering that more than 80% of these species were described by one man, the Austrian Dr Max Beier, between 1932 and 1966. However, that is virtually the sum of our knowledge of pseudoscorpion diversity in South Africa. We sorely lack detailed biological and ecological data on most species, as most literature on the South African fauna involves either brief species descriptions or species lists. Also, nearly all species were described by foreign scientists, with the result that only a few type specimens were deposited at South African institutions, which makes comparison of material difficult.
To remedy this situation a long-term project has been initiated with the aim of revising our entire South African pseudoscorpion fauna. Luckily, recent research has brought both the taxonomy and phylogeny of pseudoscorpions into the modern age. A multinational collaboration between South African institutions (such as the National Museum in Bloemfontein, the Iziko South African Museum in Cape Town, the KwaZulu-Natal Museum in Pietermaritzburg, the University of the Free State and the National Collection of Arachnida at the Agricultural Research Council) and overseas institutions (such as the Western Australian Museum and the Zoological Museum of Hamburg) has already resulted in the revision of the first South African pseudoscorpion family. Using a holistic approach that combined morphological, molecular and zoogeographical data, the species of the family Geogarypidae were revised. The results are currently being prepared for publication and the effort has already paid off with the discovery of nine previously unknown species, thus doubling the species count within the family. Preliminary work has also been done on the second family, Gymnobisiidae, with the effort already yielding four previoulsy unknown species to add to the two already known ones. The aim of this study is to produce a series of research articles that will be the most comprehensive summary of the more than 100 years of research done on South African pseudoscorpions.
Aguiar, N.O. & Bührnheim, P.F. 1998. Phoretic pseudoscorpions associated with flying insects in Brazilian Amazônia. Journal of Arachnology 26: 452-459.
Beier, M. 1958. Pseudoscorpionidea (false scorpions) of Natal and Zululand. Annals of the Natal Museum 14: 155-187.
Harvey, M.S. 1992. The phylogeny and classification of the Pseudoscorpionida (Chelicerata: Arachnida). Invertebrate Taxonomy 6: 1373-1435.
Legg, G. 2008. Taxonomy and the dangers of sex with special reference to pseudoscorpions. Monographs 12: 247-257.
Murienne, J., Harvey, M.S. & Giribet, G. 2008. First molecular phylogeny of the major clades of Pseudoscorpiones (Arthropoda: Chelicerata). Molecular Phylogenetics and Evolution 49: 170-184.
Tizo-pedroso, E. & Del-Claro, K. 2005. Matriphagy in the neotropical pseudoscorpion Paratemnoides nidificator (Balzan 1888) (Atemnidae). Journal of Arachnology 33: 873-877.
Zeh, J.A. & Zeh, D.W. 1990. Cooperative foraging for large prey by Paratemnus elongatus (Pseudoscorpionida: Atemnidae). Journal of Arachnology 18: 307-311.
A pseudoscorpion of the suborder Neobisioidea in leaf litter. (Photo: Mark Hedin)
A longhorn beetle impaled on a thorn by a shrike, with a ‘traveling’ Titanatemnus natalensis pseudoscorpion still attached to it. (Photo: Charles R. Haddad)
Female Ellingsenius sculpturatus, a species found in beehives. (Photo: J.A. Neethling)