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The spider family Segestriidae includes 119 described species, seven of which occur in North America north of Mexico (Ubick 2005; Platnick 2014). In the United States, Ariadna bicolor is the most widespread species, ranging from Maine to central Florida and west to southern California. The three other Ariadna species in the U.S. have restricted distributions there: Ariadna arthuri is found in southern Florida, Ariadna pilifera is found in Arizona, and Ariadna fidicina is found along the coast of southern California. The other segestriid genus found in the U.S., Segestria, is mainly Palearctic (Giroti and Brescovit 2011) and in North America is known only from the Pacific coast, with one species, Segestria pacifica, found from Baja California to Canada and two narrowly distributed species, Segestria bella and Segestria cruzana, known from central California and Santa Cruz Island, respectively. Ubick (2005) noted also that an undetermined Segestria species had recently been found in New Mexico. (Ubick 2005)

Segestriids have six eyes arranged in three groups that are positioned near the front of the head region. The cephalothorax and abdomen are both longer than wide. Segestriids have the unusual habit of resting with six legs extended forward and just the last pair backward. These spiders are nocturnal sedentary hunters that live in crevices. They can be abundant in appropriate habitat, such as in rock walls, rock talus, and under loose tree bark (especially Eucalyptus). Segestriids build round, tubular, silk-lined retreats, often positioned at the broken end of a branch, in dead wood, or among debris on the ground. There is elaborate webbing at the retreat entrance and a number of signal lines radiate out from the central tube, a pattern reminiscent of the often larger webs of filistatids such as Kukulcania (Filistatidae). The signal lines are monitored by the spider's legs, including the anteriorly (forward) directed 3rd pair of legs, and provide information about the position and size of approaching prey, which the spider captures and pulls into its retreat (Comstock 1940 includes both a description and a photograph showing signal lines; Bradley 2013). Henschel (1995) reported that Ariadna spiders in the Namib Desert gravel plains typically place seven or eight stones in a circle around their burrow entrance and concluded that these stones help the spiders detect accessible prey as they brush past the stones.

Segestriids do well in captivity, accepting a range of insect prey, and can live for several years (Ubick 2005).

Segestriids are closely related to the Dysderidae, Oonopidae, and Orsolobidae. Ubick (2005) briefly reviewed the limited taxonomic literature on Nearctic segestriids and emphasized the need for a modern revision of the family in North America.


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