A primer on pseudoscorpions and taxonomic status in Canada |
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General information and editorial notes News and Notes Activities at the Entomological Societies' meeting Summary of the Scientific Committee meeting Project Update: Forest Arthropods Profile of Entomologists in Survey's Annotated List of Workers A primer on pseudoscorpions and taxonomic status in Canada First BSC Biodiversity Scholarship awarded Arctic Corner Arctic and Boreal Entomology Course 2004 Call for information on insect research in Canada's arctic Requests for Material or Information Invited
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Chris Buddle [a pdf version of this article is available by clicking here] Introduction The arachnid order Pseudoscorpiones, commonly known as pseudoscorpions, false scorpions, or book scorpions, represent an important yet understudied Arachnid order. Harvey (2002) placed the order among a list of ‘neglected cousins’ of the Arachnida, in an attempt to highlight the need for more intensive research on the smaller arachnid orders. The pseudoscorpions comprise about 3.3% of the described arachnid species (Harvey 2002), with just over 3,000 known species, globally (Harvey 1990), and about 350 species are known from North America north or Mexico (Coddington et al. 1990). Although this diversity pales in comparison to many other arthropod orders, pseudoscorpions are nevertheless ecologically important, morphologically and taxonomically distinct, and efforts are required to better understand the biology, ecology, and taxonomy of these curious arachnids. In North America, despite incredible work by some arachnologists in the mid- to late 1900s (e.g. E. Benedict, C. Hoff, S. Nelson, W. Muchmore), we know embarrassingly little about the distribution, ecology and taxonomy of pseudoscorpions in much of the northern half of the continent. I have begun a long-term inventory of pseudoscorpions in Canada, and the first step, reported here, is to document what species are presently known to occur in the country, and to speculate on their distributions. Future efforts will be directed at producing an identification guide to pseudoscorpions of Canada, and subsequent taxonomic and ecological studies. This is especially important now, since William Muchmore, the current expert on Pseudoscorpiones in North America, has been retired for many years, and personal communications with him have indicated he has almost completely wrapped up his life’s work on this group. Description Pseudoscorpions are small (typically less than 5 mm in length) predacious arachnids, with a general similarity to true scorpions, but without the tail. They are generally light tan to reddish brown to black in colour and are typically compressed dorsoventrally. They have two main body parts, divided into an anterior prosoma or cephalothorax and a posterior opisthosoma or abdomen. The dorsal surface of the cephalothorax shows little signs of segmentation, whereas the abdomen is divided by 11 or 12 clearly defined segments. The chelicerae of pseudoscorpions are two-segmented structures attached close together under the anterior margin of the carapace; these are used to grasp and macerate food, and the opening to the silk glands (located in the cephalothorax) are near the end of the movable finger of each chelicera. The first pair of ‘leg-like’ appendages of pseudoscorpions are the long and conspicuous pedipalps, which each bear the distinctive chela used to grasp prey or defend against predators. The remaining four pairs of appendages are the walking legs. Life history, ecology, and taxonomy The life-cycle of pseudoscorpions is straightforward, although the pre-mating courtship routine is highly complex in some species (Weygoldt 1969). Males produce a stalked spermatophore which is attached to a substrate and subsequently taken up by a female. Fertilized eggs are retained in a secreted pouch attached to the female’s abdomen, and young remain in the brood pouch until the first nymphal stage. Pseudoscorpions go though three nymphal stages (the protonymph, deutonymph and tritonymph) before molting to sexually mature adults. Males of some species (e.g., Microbisium, see Photograph 1) are rare, causing some speculation that parthenogenesis may occur within the group (Hoff 1949, Muchmore 1990a). Adults are believed to be relatively long-lived in the field (6 months or more) (Hoff 1949), and can survive in captivity for more than one year (Weygoldt 1969). Microbisium
brunneum (Hagen) collected from moss in spruce forest in Parc d’Aiguebelle,
Québec (region of Abitibi-Témiscamingue) (June 2004, collector: C.
Buddle) (photograph by C. Buddle) (click picture to
enlarge) Pseudoscorpions are cryptic animals, living amongst
leaf-litter, under rocks, within compost piles, under bark and within
decaying wood, in caves, and in various vertebrate nests. Many species are
also phoretic on insects or birds. Species such as Chelifer cancroides
(L.) (Photograph 2) are cosmopolitan, typically found in houses, barns or
other human-made structures. Like many arachnids, pseudoscorpions are
believed to be generalist predators, feeding upon small soil invertebrates
(e.g., mites, Collembola), various Diptera, ants, and occasionally
caterpillars. The general ecology of the group has been vastly understudied
(see Muchmore 1973), although two recent papers by Bell et al. (1999) and
Yamomoto et al. (2001) suggest the group may be useful biological
indicators. These studies support the hypothesis that ground-dwelling
pseudoscorpions are dependent on well-developed litter, which means some
dependence on older/abandoned forest stands (Yamomoto et al. 2001), or
hedgerows in an agricultural setting (Bell et al. 1999). Although the
densities of pseudoscorpions are sometimes quite high, I have found their
populations to be extraordinarily patchy or clumped. One litter sample, for
example, may yield a dozen or more specimens, whereas most may yield none. I
suspect this patchy distribution, along with the difficult taxonomy (see
below), explains the paucity of ecological studies on the group. Some
aspects of pseudoscorpion behaviour, sexual selection, and dispersal,
however, have been well-studied in the neotropics (e.g., Zeh and Zeh 1992),
and this example has even found its way to popular science writing (Judson
2002). The most recent phylogenetic treatment of the order was
completed by Harvey (1992), and key references for the pseudoscorpions in
North America are Muchmore (1990a), Hoff (1949), Nelson (1975), and
Chamberlin (1931). Pseudoscorpion taxonomy is difficult; it relies on
careful specimen preparation, and the characters are often highly conserved,
or depend on size or shape of certain structures (e.g. Nelson 1984).
However, it is possible to overcome these obstacles, and Muchmore (1990a)
provides a reasonably complete key to genera of pseudoscorpions occurring in
North America. This key, however, requires considerable cross referencing
with taxonomic publications, and voucher specimens are required to properly
assess character states for more difficult couplets. Collection and Preservation Pseudoscorpions can be preserved in 70% ethanol, and later studied under a dissection microscope. Some dissection and clearing is required for examination of specimens for taxonomic purposes. In most cases, a chela, pedipalp chelicera and one leg I and one leg IV are removed from the specimen. Temporary slide mounts can be made using lactic acid, but permanent slide mounts are required for voucher specimens. Hoff (1949) and Nelson (2005) provide details about specimen preparation and examination. Status in Canada The first synopsis of pseudoscorpion species in Canada was provided by Dondale (1979), who reporting five species in the country based on Hoff (1958) and Kaisila (1964). Sharkey’s (1980) unpublished report, together with more recent publications (e.g., Koponen and Sharkey 1988; Muchmore 1990b), keys (Muchmore 1990a) and Harvey’s (1990) catalog document 7 families, and 23 valid known species from Canada (Table 1), and at least three undescribed species. Provincial records will rise quickly with additional collections and after identifications of specimens in my collection are complete. For example, the common boreal species Microbisium brunneum (Hagen) (Photograph 1) is likely present in all provinces and territories as will be the easily recognized C. cancroides (Photograph 2) – most questions from the general public about pseudoscorpions are in reference to this cosmopolitan species, often found crawling on the walls of older homes, particularly in humid locations. At present, only three species have been recorded from higher latitudes: Syarinus obscurus (Banks) (Yukon Territory, unpublished record from V. Mahnert), Wyochernes arcticus Muchmore (Yukon Territory) (Muchmore 1990b), and M. brunneum from northern Québec (Koponen and Sharkey 1988). These records severely under represent the true richness of pseudoscorpions in Canada, as at least 30 species are known from locations in the USA adjacent to Canadian provinces (Harvey 1990), and many of these will likely be documented in Canada with future collections and inventory work. I suspect upwards of 50 species will eventually be recorded from Canada.
Conclusions Pseudoscorpions are remarkable arthropods, well deserving of more research. Taxonomic work is still required for many North American families (Coddington et al. 1990), and regional keys to species will certainly simplify their inclusion in biodiversity studies. Ecological work is also desperately needed, but again relies on accessible taxonomy. I will continue working on this group of arachnids, and would greatly appreciate any specimens, along with detailed habitat and locality information.
Table
1. Summary of pseudoscorpion
families and species recorded in
References Bell, J.R., S. Gates, A.J. Haughton, D.W. Macdonald, H. Smith, C.P. Wheater, and W.D. Cullen. 1999. Pseudoscorpions in field margins: effects of margin age, management and boundary habitats. Journal of Arachnology 27: 236-240. Chamberlin, J.C. 1931. The arachnid order Chelonethida. Stanford University Publication of Biological Science 7: 1-284. Coddington, J.A., S.F. Larcher, and J.C. Cokendolpher. 1990. The systematic status of Arachnida, exclusive of Acari, in North America north of Mexico, pp. 5-20 in Kosztarab, M., and C.W. Shaefer (Eds). Systematics of the North American Insects and Arachnids. Virginia Agricultural Experimental Station Information Series 90-1. Virginia Polytechnic Institute and State University, Blacksburg. Dondale, C.D. 1979. Opiliones, Pseudoscorpionida, Scorpionida, Solfugae. pp. 250-251 in Danks H.V., (Ed.) Canada and its insect fauna. Memoirs of the Entomological Society of Canada 108. Harvey M.S. 1990. Catalogue of the Pseudoscorpionida (Mahnert V, Ed.). Manchester University Press. Harvey, M.S. 1992. The phylogeny and classification of the Pseudoscorpionida (Chelicerate: Arachnida). Invertebrate Taxonomy 6: 1373-1435. Harvey M.S. 2002. The neglected cousins: What do we know
about the smaller Arachnid orders? Hoff, C.C. 1949. The pseudoscorpions of Illinois. Bulletin of the Illinois Natural History Survey 24: 413-498. Hoff C.C. 1958. List of the Pseudoscorpions of North America North of Mexico. American Museum Novitates 1875: 1-50. Judson, O. 2002. Dr. Tatiana’s Sex Advice to all Creation. Henry Holt and Company. New York, New York. Kaisila J. 1964. Some pseudoscorpions from Newfoundland. Annales Zoologici Fennici 1: 52-54. Koponen S. and M.J. Sharkey. 1988. Northern records of Microbisium brunneum (Pseudoscorpionida, Neobisiidae) from eastern Canada. Journal of Arachnology 16: 388-390. Muchmore, W.B. 1973. Ecology of pseudoscorpions: a review. pp. 121-127 in Dindal, D.L., (Ed.). Proceedings of the First Soil Microcommunities Conference. Syracuse, New York. Muchmore, W.B. 1990a. Pseudoscorpionida. pp 503-527 in Dindal D.L. (Ed.). Soil Biology Guide. John Wiley & Sons. Muchmore, W.B. 1990b. A pseudoscorpion from arctic Canada (Pseudoscorpionida: Chernetidae). Canadian Journal of Zoology 68: 389-390. Nelson, S., Jr. 1975. A systematic study of Michigan Pseudoscorpionida (Arachnida). American Midland Naturalist 93: 257-301. Nelson, S., Jr. 1984. The pseudoscorpion genus Microbisium in North and Central America (Pseudoscorpionida, Neobisiidae). Journal of Arachnology 12: 341-350. Nelson, S., Jr. 2005. Pseudoscorpions. Entomology Note #16, Michigan Entomological Society. Published at:http://insects.ummz.lsa.umich.edu/MES/notes/entnote16.html [accessed 13 January 2005]. Sharkey, M.J. 1980. A preliminary report on the pseudoscorpions of Canada. Unpublished Report. Weygoldt, P. 1969. The Biology of Pseudoscorpions. Harvard University Press, Cambridge, Massachusetts. Yamamoto, T., N. Nakagoshi, and Y. Touyama. 2001. Ecological study of pseudoscorpion fauna in the soil organic layer in managed and abandoned secondary forests. Ecological Research 16: 593-601. Zeh, D.W., and J.A. Zeh. 1992. Dispersal-generated sexual selection in a beetle-riding pseudoscorpion. Behavioral Ecology and Sociobiology 30: 135-142.
Acknowledgements: H. Proctor, M. Sharkey, W. Muchmore, and V. Mahnert kindly provided unpublished records. Discussions with J. Bell, W. Muchmore, J. Cokendolpher, M. Harvey, and M. Judson have been inspiring and extremely helpful in this endeavor. Thanks also to numerous people for providing me with pseudoscorpion specimens from across Canada.
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