The spider family Pimoidae (large hammockweb spiders) includes just 37 described species in four genera (Nanoa, 1 species; Pimoa, 27 species; Putaoa, two species; Weintrauboa, seven species) (Platnick 2013). Fourteen of these species (Nanoa enana and 13 Pimoa) occur in North America north of Mexico, where they are found along the western edge of the continent between the 35th and 60th parallels, including the Sierra Nevada and Cascades, Idaho, and western Montana (Bitterroot Range) (Hormiga and Lew 2005; Platnick 2013). More broadly, the pimoids have a discontinuous distribution that includes the west coast of North America; Europe (the Alps and Apennines, and Cantabrian Mountains); and Asia (the Himalayas and adjacent areas and Japan) (Hormiga 1994, 2003; Wang et al. 2008).
Pimoidae is the sister group to Linyphiidae (Arnedo et al. 2009 and references therein; Michalik and Hormiga 2010) and members of these two families closely resemble each other in general appearance. Some tetragnathids, e.g., in the genus Meta, are also similar to Pimoa, but the orb webs made by tetragnathids make them easy to distinguish from pimoids. Larger members of the hahniid genus Calymmaria with annulated (ringed) legs can be confused with Pimoa in the field, especially since they are found in similar habitats and are common across much of the range of Pimoa in North America. (Hormiga and Lew 2005)
Pimoids build large, flat or slightly sagging sheet webs close to the ground, typically in humid areas (in some species, the web may be more than a square meter in area) in sheltered microhabitats such as fallen or hollow tree trunks and under overhanging cornices in banks and road cuts. Pimoids are sometimes found in human-made structures such as sheds and outhouses and several species can be found in caves (Wang et al. 2008). Pimoids hunt on their webs at night, spending the daylight hours hiding in a retreat on the margin of the web. Like linyphiids, pimoids hang from the underside of their webs; they attack prey by grasping it from below through the sheet. Pimoid webs are often maintained for long periods of time and can show obvious signs of repair and degradation. (Hormiga and Lew 2005; Bradley 2013)
The Pimoidae form a relictual group along the western coast of North America, Europe (Alps, Apennines and Cantabrian Mountains of northern Spain) and the Himalayas. This makes a holarctic predecessor probable. In 2003, a species was found in Japan. The species Pimoa cthulhu, described by Gustavo Hormiga in 1994, is named for Howard Phillips Lovecraft's mythological deity Cthulhu.