The Wolf Spiders, Nurseryweb Spiders, and Lynx Spiders of Canada and Alaska
The spiders treated in this book are the only Canadian representatives of a group known as the three-clawed hunters (Gertsch 1979). All of the Canadian forms live as wandering hunters, taking prey on the ground by stealth. They all possess, to some degree, a third or median claw at the tip of each leg tarsus. This third claw enables web-building spiders to walk and climb on aerial webs, and its reduction is apparently a consequence of the loss, in hunting spiders, of dependence on silken webs. This process has apparently occurred independently among the wolf spiders, the nurseryweb spiders, and the lynx spiders, for web builders occur in each of the three families in warmer parts of the world.
These spiders can be identified to family level by means of the key published in Part 5 of this series (Dondale and Redner 1978). The three families share the peculiar shape of the tapetum, which is a layer of light-reflecting cells within the secondary pairs of eyes (anterior lateral, posterior median, and posterior lateral eyes). Whereas in most spiders the tapetum takes the shape of a canoe, in the groups treated here it has the shape of a grate, or lattice. The closest relatives of the wolf spiders are probably the nurseryweb spiders, but the relationships of the lynx spiders to the other two groups are not yet known.