I can't imagine how the OP found one, let alone many, in North America.
http://en.wikipedia.org/w/index.php?title=Yellow_sac_spider&redirect=no
Yellow sac spider
From Wikipedia, the free encyclopedia
Distribution
Cheiracanthium is primarily an Old World genus, with many species found from northern Europe to Japan, from Southern Africa to India and Australia. The only known species in the New World are C. inclusum and C. mildei. While the former also occurs in Africa and Runion, the latter is found in the Holarctic region and Argentina. They can also be found in the lower mainland of British Columbia, Canada [2]
http://en.wikipedia.org/w/index.php?title=Yellow_sac_spider&redirect=no
Yellow sac spider
From Wikipedia, the free encyclopedia
Distribution
Cheiracanthium is primarily an Old World genus, with many species found from northern Europe to Japan, from Southern Africa to India and Australia. The only known species in the New World are C. inclusum and C. mildei. While the former also occurs in Africa and Runion, the latter is found in the Holarctic region and Argentina. They can also be found in the lower mainland of British Columbia, Canada [2]
