The spider family Philodromidae (running crab spiders) includes 542 described species, nearly a hundred of which are known from North America north of Mexico (Philodromus dispar is native to Europe and Central Asia, but has been introduced to the United States and Canada) (Platnick 2013).
Philodromids are two-clawed, flat-bodied, somewhat crab-like hunting spiders (Dondale 2005). Like thomisids, many species hold their legs in a laterigrade position (i.e., the legs extend sidewise and the femora, especially, are twisted so that the front surface faces up). The eight eyes are at the front of a narrow cephalic region (i.e., the forward part, or "head" region, of the cephalothorax) and the cephalothorax is broad and often as wide as it is long. These spiders were formerly considered to comprise a subfamily of Thomisidae, but Homann (1975, cited in Dondale 2005) concluded that they were independent of the thomisids, a finding confirmed by the molecular phylogenetic analysis by Benjamin et al. (2008). In comparison with philodromids, thomisids tend to have more compact and globose bodies, with thicker legs; raptorial spines on the first pair of legs; prominent eye tubercles ("bumps"); and no claw tufts or scopulae, or distinct brushes of hair, on their legs.
Philodromids lead an active predatory lifestyle on plant stems and leaves. Some are found only on coniferous trees, others only on deciduous trees; a small number live in deserts. Life histories have been studied by Dondale (1961) and Putnam (1967) and Haynes and Sisojevic (1966) studied predatory behavior. Dondale (1964, 1967) used courtship behavior to distinguish some closely related species.
(Dondale 2005; Bradley 2013)
- Benjamin, S.P., D. Dimitrov, R.G. Gillespie, and G. Hormiga. 2008. Family ties: molecular phylogeny of crab spiders (Araneae: Thomisidae). Cladistics 24: 708-722.
- Bradley, R.A. 2013. Common Spiders of North America. University of California Press, Berkeley.
- Dondale, C.D. 1961. Life histories of some common spiders from trees and shrubs in Nova Scotia. Canadian Journal of Zoology 39: 777-787.
- Dondale, C.D. 1964. Sexual behaviour and its application to a species problem in the spider genus Philodromus (Araneae: Thomisidae). Canadian Journal of Zoology 42(5): 817-827.
- Dondale, C.D. 1967. Sexual behaviour and the classification of the Philodromus rufus complex in North America (Araneae: Thomisidae). Canadian Journal of Zoology 45(4): 453-459.
- Dondale, C.D. 2005. Philodromidae. Pp. 192-193 in D. Ubick, P. Paquin, P.E. Cushing, and V. Roth (eds.) Spiders of North America: an Identification Manual. American Arachnological Society.
- Dondale, C.D. and J.H. Redner. 1968. The imbecillus and rufus groups of the spider genus Philodromus in North America (Araneida: Thomisidae). Memoirs of the Entomological Society of Canada No. 55. 78 pp.
- Dondale, C.D. and J.H. Redner. 1969. The infuscatus and dispar groups of the spider genus Philodromus in North and Central America and the West Indies. The Canadian Entomologist 101(9): 921-954.
- Dondale, C.D. and J.H. Redner. 1975a. The fuscomarginatus and histrio groups of the spider genus Philodromus in North America (Araneida: Thomisidae). The Canadian Entomologist 107(4): 369-384.
- Dondale, C.D. and J.H. Redner. 1975. Revision of the spider genus Apollophanes (Araneida: Thomisidae). The Canadian Entomologist 107: 1175-1192.
- Dondale, C.D. and J.H. Redner. 1976. A review of the spider genus Philodromus in the Americas (Araneida: Philodromidae) The Canadian Entomologist 108: 127-157.
- Dondale, C.D. and J.H. Redner. 1978. The crab spiders of Canada and Alaska (Araneae: Philodromidae and Thomisidae). The Insects and Arachnids of Canada. Part 5. Agriculture Canada, Ottawa. Publication 1663. 255 pp.
- Dondale, C.D., A.L. Turnbull, and J.H. Redner. 1964. Revision of the Nearctic species of Thanatus C.L. Koch (Araneae: Thomisidae). The Canadian Entomologist 96: 636-656.
- Haynes, D.L. and P. Sisojevic. 1966. Predatory behaviour of Philodromus rufus Walckenear (Araneae: Thomisidae). The Canadian Entomologist 98(2): 113-133.
- Homann, H. 1975. Die Stellung der Thomisidae und der Philodromidaeim System der Araneae (Chelicerata, Arachnida). Zeitschrift fur Morphologie und Ökologie der Tiere 80: 181-202.
- Marusik, Y.M. 1989. Two new species of the spider genus Xysticus and synonymy of crab spiders (Aranei, Thomisidae, Philodromidae) from Siberia. Zoologicheskii Zhurnal 68(4): 140-145.
- Platnick, N. I. 2013. The world spider catalog, version 14.0. American Museum of Natural History, online at http://research.amnh.org/entomology/spiders/catalog/index.html
- Putnam, W.L. 1967. Life histories and habits of two species of Philodromus (Araneida: Thomisidae) in Ontario. The Canadian Entomologist 99: 622-631.
- Sauer, R.J. and N.I. Platnick. 1972. The crab spider genus Ebo (Araneida: Thomisidae) in the United States and Canada. The Canadian Entomologist 104(1): 35-60.
- Schick, R.X. 1965. The crab spiders of California (Araneida: Thomisidae). Bulletin of the American Museum of Natural History 129(1): 1-180.
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