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The spider family Selenopidae (wall crab spiders or flatties) includes 252 described species (Platnick 2014). The family has a pantropical distribution, although much of the known diversity is found in Africa and Australia; only Selenops occurs in the New World (Crews and Harvey 2011; Platnick 2014). Several selenopid species are found in deserts and selenopids can be found from sea level to over 2500 meters (Crews and Harvey 2011). The majority of selenopid species are placed in the genus Selenops, which is found in the tropics and subtropics worldwide (Crews 2011). Selenops are relatively large (adult body size 5 to 20 mm), but are among the most secretive and elusive of spiders due to their speed (up to 63 body lengths/second for Selenops lindborgi) and their ability to hide in inaccessible places (Muma 1953; Crews et al. 2008). In North America north of Mexico, the six or seven recognized species occurring in this region are found from southern California east to Texas, Florida, and most Caribbean islands (Crews 2011; Platnick 2014).
Selenopids are extremely dorsiventrally (top-to-bottom) flattened and are exceptional in their running and striking speeds, which place them amongst the world’s fastest animals (Crews et al. 2008; Crews 2011). They have eight eyes, outlined in black, at the front of the wide face. Typically, six eyes are in what appears to be one row, the outermost eyes being the smallest; just behind and lateral to these are the last pair of eyes, which are often the largest and facing to the side. The legs are held in a laterigrade position (i.e., the legs extend sidewise and the femora, especially, are twisted so that the front surface faces up), which helps selenopids fit their flattened bodies into very narrow spaces. (Crews 2005; Bradley 2013)
Selenopids live in habitats ranging from dry desert and chaparral to mesic (moist) tropical areas. They are typically found under rocks and bark, but can also be found in houses and occasionally on logs, in debris on the ground, or between the bases of leaves of tropical plants (Muma 1953). Selenopids are nocturnal and do not build webs. Although they can be challenging to collect, selenopids are easily reared in the lab on crickets and fruitflies. Adults have been collected throughout the year. (Crews 2005)
Crews et al. (2008) reported on the natural history of Selenops occultus in Brazil as well as various Caribbean species.