Philodromus

Philodromus aureolus, copyright Donald Hobern.

Belongs within: Philodromidae.

The running of the crabs
Published 23 August 2019

There are many varieties of spider in the world that, while not necessarily uncommon, tend to be little known to the general public owing to their cryptic and retiring nature. As an example, meet the genus Philodromus.

Philodromus cespitum, copyright R. Altenkamp.

Philodromus is the largest genus recognised in the family Philodromidae, commonly referred to as the running crab spiders or small huntsman spiders. About 250 species have been assigned to this genus from various parts of the world (Muster 2009), mostly in the Holarctic region. Like the huntsman spiders of the Sparassidae and the crab spiders of the Thomisidae, philodromids are an example of what old publications often referred to as ‘laterigrade’ spiders, in which the legs are arranged to extend sideways from the body more than forwards and backwards. They have eight eyes arranged in two recurved rows of four. Philodromids differ from crab spiders in having scopulae (clusters of hairs that can look a bit like little booties) on the leg tarsi, and having secondary eyes that lack a tapetum (reflective layer). They differ from huntsmen in that the junction between the tarsi and metatarsi is restricted to movement in a single plane, rather than the tarsus being able to move freely (Jocqué & Dippenaar-Schoeman 2007). Philodromids do not build a web to capture prey but instead seize prey directly.

The distinction between Philodromus and other genera in the family has historically been imprecise (Muster 2009) which goes some way to explaining the large number of species it has encompassed. In general, though, the eye rows of Philodromus are relatively weakly recurved, and its body form is less slender than that of the genera Tibellus and Thanatus. These may well be primitive features for the family, and a phylogenetic analysis of philodromids by Muster (2009) indicated that at least one group of species historically included in Philodromus (the P. histrio group) may be more closely related to the slender-bodied genera. The great French arachnologist Eugene Simon recognised several species groups in Philodromus, distinguished by features such as eye arrangement and leg spination, but recent authors feel that the status of these groups requires further investigation before we could consider treat?ing them as distinct genera.

Philodromus dispar, copyright Judy Gallagher.

Most species of Philodromus live on vegetation, flattening themselves against stems and foliage to avoid detection. As with other laterigrade spiders, the arrangement of their legs allows for rapid sideways movement, perfect for avoiding predators or turning up where prey do not expect them. At least one species group found in the Mediterranean region (including P. pulchellus and its relatives) differs in being ground-living, with a predilection for salt flats (Muster et al. 2007). Bites to humans from Philodromus appear to be vanishingly rare: a report on such a bite by Coetzee et al. (2017) appears to be the first record of one (the bite was painful, causing swelling and some ulceration, but without long-term effects following treatment). Philodromus species are much more likely to have a net positive value to humans, as they may act as control agents for insect pests among crops and orchards.

Systematics of Philodromus
<==Philodromus Walckenaer 1826JD-S07
    |--P. alascensis Keys. 1883S06
    |--P. assamensis Tikader 1962T72
    |--P. aureolus (Ol. 1789)S06
    |--P. betrabatai Tikader 1966T72
    |--P. bhagirathai Tikader 1966T72
    |--P. blandus Koch 1880S06
    |--P. caespiticola (Walck. 1805)S06
    |--P. calidus Lucas 1846E12
    |--P. californicusMC02
    |--P. cespitum (Walckenaer 1802)BBM02
    |--P. collinus Koch 1835BH02
    |--P. corticinus (Koch 1837)K55
    |--P. decoratus Tikader 1962T72
    |--P. devhutai Tikader 1966T72
    |--P. diardi Doleschall 1859D59
    |--P. dispar Walckenaer 1826BH02
    |--P. domesticus Tikader 1962T72
    |--P. emarginatus (Schrk. 1803)S06
    |--P. exilisJDW90
    |--P. fallaxK01
    |--P. fuscolimbatus Lucas 1846E12
    |--P. fuscomarginatus (D. G. 1778)S06
    |--P. gracilentus Lucas 1846E12
    |--P. histrio (Latr. 1819)S06
    |--P. imbecillusWY88
    |--P. kendrabati Tikader 1966T72
    |--P. maliniae Tikader 1966T72
    |--P. mohiniae Tikader 1966T72
    |--P. oblongiusculus Lucas 1846E12
    |--P. ornatus Lucas 1846E12
    |--P. pernix Blackwall 1846PS08
    |--P. placidus Bansk 1892PS08
    |--P. poecilus (Th. 1872)S06
    |--P. pulchellus Lucas 1846E12
    |--P. rufusPS08
    |    |--P. r. rufusPS08
    |    `--P. r. quartus Dondale & Redner 1968PS08
    |--P. shillongensis Tikader 1962T72
    `--P. vulgarisR14
Nomina nuda: Philodromus nebulosusS06
             Philodromus turneriS06

*Type species of generic name indicated

References

[BH02] Bell, J. R., A. J. Haughton, N. D. Boatman & A. Wilcox. 2002. Do incremental increases of the herbicide glyphosate have indirect consequences for spider communities? Journal of Arachnology 30 (2): 288–297.

[BBM02] Bonte, D., L. Baert & J.-P. Maelfait. 2002. Spider assemblage structure and stability in a heterogeneous coastal dune system (Belgium). Journal of Arachnology 30 (2): 331–343.

Coetzee, M., A. Dippenaar, J. Frean & R. H. Hunt. 2017. First report of clinical presentation of a bite by a running spider, Philodromus sp. (Araneae: Philodromidae), with recommendations for spider bite management. South African Medical Journal 107 (7): 576–577.

[D59] Doleschall, C. L. 1859. Tweede Bijdrage tot de kennis der Arachniden van den Indischen Archipel. Verhandelingen der Natuurkundige Vereeniging in Nederlandsch Indie [Acta Societatis Scientiarum Indo-Neêrlandicae] 5 (5): 1–60, pls 1–18.

[E12] Evenhuis, N. L. 2012. Publication and dating of the Exploration Scientifique de l’Algérie: Histoire Naturelle des Animaux Articulés (1846–1849) by Pierre Hippolyte Lucas. Zootaxa 3448: 1–61.

[JDW90] Jennings, D. T., J. B. Dimond & B. A. Watt. 1990. Population densities of spiders (Araneae) and spruce budworms (Lepidoptera, Tortricidae) on foliage of balsam fir and red spruce in east-central Maine. Journal of Arachnology 18: 181–194.

[JD-S07] Jocqué, R., & A. S. Dippenaar-Schoeman. 2007. Spider Families of the World. Royal Museum for Central Africa: Tervuren (Belgium).

[K55] Kraus, O. 1955. Spinnen von Korsika, Sardinien und Elba (Arach., Araneae). Senckenbergiana Biologica 36: 371–394.

[K01] Kulczyński, V. 1901. Arachnoideák [Arachnoidea]. In: Horváth, G. (ed.) Zichy Jenő Gróf Harmadik Ázsiai Utazása [Dritte Asiatische Forschungsreise des Grafen Eugen Zichy] vol. 2. Zichy Jenő Gróf Harmadik Ázsiai Utazásának Állattani Eredményei [Zoologische Ergebnisse der Dritten Asiatischen Forschungsreise des Grafen Eugen Zichy] pp. 311–369. Victor Hornyánszky: Budapest, and Karl W. Hierseman: Leipzig.

[MC02] Miliczky, E. R., & C. O. Calkins. 2002. Spiders (Araneae) as potential predators of leafroller larvae and egg masses (Lepidoptera: Tortricidae) in central Washington apple and pear orchards. Pan-Pacific Entomologist 78 (2): 140–150.

Muster, C. 2009. Phylogenetic relationships within Philodromidae, with a taxonomic revision of Philodromus subgenus Artanes in the western Palearctic (Arachnida: Araneae). Invertebrate Systematics 23: 135–169.

Muster, C., R. Bosmans & K. Thaler. 2007. The Philodromus pulchellus-group in the Mediterranean: taxonomic revision, phylogenetic analysis and biogeography (Araneae: Philodromidae). Invertebrate Systematics 21: 39–72.

[PS08] Pinzón, J., & J. Spence. 2008. Performance of two arboreal pitfall trap designs in sampling cursorial spiders from tree trunks. Journal of Arachnology 36 (2): 280–286.

[R14] Ramírez, M. J. 2014. The morphology and phylogeny of dionychan spiders (Araneae: Araneomorphae). Bulletin of the American Museum of Natural History 390: 1–374.

[S06] Strand, E. 1906. Die arktischen Araneae, Opiliones und Chernetes. In: Römer, F., & F. Schaudinn (eds) Fauna Arctica. Eine Zusammenstellun der arktischen Tierformen, mit besonder Berücksichtigung des Spitzbergen-Gebietes auf Grund der Ergebnisse der Deutschen Expedition in das Nördliche Eismeer im Jahre 1898 vol. 4 pp. 431–478. Gustav Fischer: Jena.

[T72] Tikader, B. K. 1972. Spider fauna of India: catalogue and bibliography. Journal of the Bombay Natural History Society 69 (1): 91–101.

[WY88] Welbourn, W. C., & O. P. Young. 1988. Mites parasitic on spiders, with a description of a new species of Eutrombidium (Acari, Eutrombidiidae). Journal of Arachnology 16: 373–385.

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