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The mostly tropical mygalomorph spider family Ctenizidae (trapdoor spiders) includes 128 described species (Platnick 2013), 14 or 15 of them occurring in North America north of Mexico: Ummidia is found throughout the United States (10 or 11 described U.S. species but many undescribed species as well), Cyclocosmia in the southeastern U.S. (two U.S. species), and Bothriocyrtum and Hebestatis in California (one U.S. species each) (Bond and Hendrixson 2005; Bradley 2013; Platnick 2013). Ctenizids, the best known of the trapdoor-building spiders, have eight eyes, like most spiders. Analyses by Bond et al. (2012) suggest that Ctenizidae may not be a monophyletic group as currently composed.
All known North American ctenizids live in silk-lined terrestrial burrows, with burrow linings consisting of a heavy layer of parchment-like silk and packed soil. Burrows are constructed with a trapdoor (often well disguised) that is used in prey capture. The spider waits beneath a slightly ajar trapdoor and when it detects potential prey passing by, it lunges out of the burrow, bites its prey, and returns with the prey to the bottom of the burrow to feed. In the United States, ctenizid habitat ranges from the more mesic climates of the southeast to the xeric climates of California deserts. Taxonomic investigations of North American ctenizids are limited, with the exception of the revision of Cyclocosmia by Gertsch and Platnick (1975). Numerous undescribed Ummidia species are known even from the United States. (Bond and Hendrixson 2005)