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The Sac Spiders of Canada and Alaska

Part 9 in this series provides a key to spider families, a detailed treatment of the crab spiders (families Philodromidae and Thomisidae) as represented in Canada, and a glossary of anatomical terms (Dondale and Redner 1978). The present part deals with two additional families of the hunting spiders in Canada, namely, Clubionidae and Anyphaenidae, which together are called sac spiders.
The sac spiders constitute a group of two-clawed hunting spiders with a world fauna of perhaps 1500 species. They have been treated as a single family by many workers, but are treated separately here in view of the qualitative differences in tracheation and in the setae forming the claw tufts (see Comments under both families).
The term "sac spiders" derives from the construction by many of these spiders of flattened tubular retreats of dense white silk; the sacs are usually made in rolled leaves or under bark. Many of the members of this group are nocturnal, spending the daylight hours in the sac, whereas others are active in daylight or darkness and live mainly in the dimness between layers of plant litter in forests, bogs, or swamps. They are swift runners, and take their prey by suddenly moving upon and seizing it with their stout toothed chelicerae.