The spider (Cheiracanthium inclusum) is small and pale beige to yellow, often with a tinge of green. A distinctive darker lance-shaped mark runs down the midline of the forward portion of the upper surface of the abdomen. The dark brown chelicerae are large, elongate, and powerful and stand out against the paler body. Body length is around 4.9 to 9.7 mm for females and 4.0 to 7.7 mm for males (Kaston 1978).
Yellow Sac Spiders are often found running about on low trees and shrubs, where they make silken tubular retreats in rolled up leaves. During the day, they typically stay hidden in these retreats, coming out at night to hunt. During the winter, their tubular retreats are built under stones and tree bark.
Yellow Sac Spidres are found throughout most of the United States, with the exception of the northern tier of states (Kaston 1978). Although it has often been stated that their bites pose a danger to humans, the bite is apparently no worse than a bee or wasp sting (Fasan et al. 2008; Vetter and Isbister 2008), although in at least some cases symptoms may be quite unpleasant (e.g., Papini 2012).
The related C. mildei, native to Europe but with records from across much of the United States, is found in houses more often than is C. inclusum.
(Howell and Jenkins 2004)
Fasan, M., A. Rennhofer, B. Moser, and G. Röggla. 2008. Spider Myths and a Case of a Bite by a Yellow Sac. Journal of the American Board of Family Medicine 21(1): 78.
Howell, W.M. and R.L. Jenkins. 2004. Spiders of the Eastern United States: a Photographic Guide. Pearson Education, Boston.
Papini, R. 2012. Documented bites by a yellow sac spider (<i>Cheiracanthium punctorium</i>) in Italy: a case report. Journal of Venomous Animals and Toxins Including Tropical Diseases 18(3): 349-354.
Vetter, R.S. and G.K. Isbister. 2008. Medical aspects of spider bites. Annual Review of Entomology 53: 409-29.