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Species Holocnemus pluchei - Marbled Cellar Spider

And Another Night Spider - Holocnemus pluchei Cellar spider - Holocnemus pluchei - male Holocnemus? - Holocnemus pluchei Spider with prey - Holocnemus pluchei Attack of the Pseuton Spiders! Victimized Fly! (Or is it an aphid? No matter.) - Holocnemus pluchei Attack of the Pseuton Spiders! Internecine Turmoil! - Holocnemus pluchei OC Cellar Spider - Holocnemus pluchei - female Cellar Spider (second of two images) - Holocnemus pluchei - female
Classification
Kingdom Animalia (Animals)
Phylum Arthropoda (Arthropods)
Subphylum Chelicerata (Chelicerates)
Class Arachnida (Arachnids)
Order Araneae (Spiders)
Infraorder Araneomorphae (True Spiders)
No Taxon (Haplogynes)
Family Pholcidae (Cellar Spiders)
Genus Holocnemus
Species pluchei (Marbled Cellar Spider)
Synonyms and other taxonomic changes
Identification
"It's the only regional pholcid with a wide, black ventral stripe that runs the length of the spider's underside." -R.J. Adams (from BugGuide comment here)

(FYI: we've also found that Crossopriza lyoni also has a somewhat dark underside.)

Abdomen elongated. The thoracic pit is very deep. Female sternum has posterior tubercle. Female palp is widened towards the tip.(1)

Male's first femur and tibia with row of short, stout spines.(2)
Range
Introduced to southwestern U.S. from the Mediterranean region.
Habitat
"Much more likely to make their webs in exposed areas compared to other pholcids." -R.J. Adams (from BugGuide comment here)
Life Cycle
Eggs are wrapped with a few strands of silk and carried in the mother's jaws until they hatch:


The egg carrying females build a distinctive spherical web around themselves:


Adults with eggs developing:
Remarks
The oldest reliable North American record known to us is an observation by W.R. Icenogle in Sutter Co., California in 1974 (S. Frommer pers. comm.). It is quite possible that Holocnemus was introduced into the state prior to 1974 but escaped attention because it superficially resembles another pholcid, Pholcus phalangioides (Fuesslin).(3)

Dr. Elizabeth Jakob has studied these spiders extensively and has published several papers on their habits and behavior. She notes in one article: "These spiders (Holocnemus pluchei) may live alone or share a sheet web with as many as 15 conspecifics of all sizes, and group membership appears to be temporally fluid..."
See Also
Pholcus phalangioides (similar body shape)
Smeringopus pallidus (similar body shape)
Print References
-Brignoli, P.M., 1971. Note sui Pholcidae d'Italia. Fragmenta Entomologica 7(2):79-101 [written in Italian, but it has genitalic diagrams; free online PDF available here]

-Porter, A.H. & E.M. Jakob, 1990. Allozyme variation in the introduced spider, Holocnemus pluchei (Araneae, Pholcidae) in California. Journal of Arachnology 18(3):313-319. [see here for free download]

-Jakob, E.M., 1994. Contests over prey by group-living pholcids (Holocnemus pluchei). Journal of Arachnology 22(1):39-45 [free 868kb PDF download available from the AAS here]
Internet References
-Images from www.spiderling.de/arages/ (spiders of Germany): images of epigynum , habitus image , another habitus image
-Many more images at EuroSpiders.com
Works Cited
1.Spiders of North America: An Identification Manual
D. Ubick, P. Paquin, P.E. Cushing and V. Roth (eds). 2005. American Arachnological Society.
2.Spider Genera of North America with Keys to Families and Genera and a Guide to Literature (2nd edition)
Vincent D. Roth. 1985. American Arachnological Society, Gainesville, Florida.
3.Allozyme variation in the introduced spider, Holocnemus pluchei (Araneae, Pholcidae) in California
Adam H. Porter & Elizabeth M. Jakob. 1990. Journal of Arachnology 18(3):313-319.