The sac spiders of the family Clubionidae[1] have a very confusing taxonomic history. Once, this family was a large catch-all taxon for a disparate collection of spiders, similar only in that they had eight eyes arranged in two rows[2] and conical anterior spinnerets that touched, and were wandering predators that built silken retreats, or sacs, usually on plant terminals, between leaves, under bark, or under rocks. These are now recognized to include several families, some of which are more closely related to the three-clawed spiders, like lynx and wolf spiders, than to Clubionidae and related families.[3]
The remnant Clubionidae now consist of a few over 500 species in 18 genera worldwide. However, "sac spider" used on its own should imply a member of the family Clubionidae, but other common names may use the phrase "sac spider" including:
In North America, the family as it is now recognised consists of only two genera, Clubiona and Elaver (formerly Clubionoides). Clubiona is nearly worldwide in distribution.