Agrarian Sac Spider and a Longlegged Sac Spider
(Cheiracanthium inclusum) (Cheiracanthium mildei)
Sac spiders can be found walking about on foliage; under leaf litter, stones, and boards; on buildings under the windowsills and siding; and in the corners of walls and ceilings within homes. C. inclusum is indigenous to much of the United States (except the northernmost states), while C. mildei , an introduced species from Europe, was found throughout much of the Northeast as of 1978. It is likely that C. mildei has substantially increased its range since that time.
Both species are of similar size (females 5 to 10 millimeters; males 4 to 8 millimeters) and coloration. C. inclusum is a light yellow to cream color with dark brown jaws (chelicerae), tips of the tarsi, and palps. C. mildei has a slightly greenish tinge to its abdomen and a pale yellow cephalothorax. The chelicerae, tarsi, and palps are similar to those of C. inclusum . Both spiders have a slightly darker dorsal stripe running lengthwise down the abdomen.
Sac spider retreats may be found outdoors under objects or indoors in the corners of walls and ceilings. These retreats are silken tubes or sacs in which the spiders hide during the daytime. In homes with light, neutral-colored walls and ceilings, the retreats may go unnoticed, as they are small and blend in with the background coloration.
The agrarian sac spiders deposit their eggs in June or July. The eggs are loosely deposited within a silken retreat, and the female remains nearby to guard them. C. inclusum is more often encountered outside; the majority of these spiders deposit their eggs on the undersides of leaves or other foliage. C. mildei is more often encountered within human-made structures and oviposits almost exclusively indoors. The young spiderlings will often remain within the silken retreat for a short period and will eventually venture out at night in search of food. The young will frequently return at daybreak to hide within the protection of the retreat.
Prowling spiders are “active hunters,” searching for prey rather than capturing it within a web. It is during these nighttime forays that the spiders encounter humans and bite when they become trapped between a person’s skin and sheets, clothing, shoes, and so forth.
These two spiders probably account for a significant number of human bites. People usually incur C. inclusum bites outdoors while gardening in the summer. C. mildei will readily bite, despite their small size, and they have been observed crawling across the human skin surface and biting without provocation. Although most of these bites are painful at the outset, they normally do not result in any serious medical conditions. For C. inclusum victims and some individuals sensitive to C. mildei , the bites will exhibit the symptoms described below.
The bite is usually very painful and burning at the outset, with developing erythema, edema, and intense itching. The burning sensation associated with the bite will last for an hour or more, and a rash and blistering will occur during the next ten hours. Some patients may exhibit systemic reactions with fever, malaise, muscle cramps, and nausea. Although there
is evidence that guinea pigs and rabbits develop necrotic lesions after bites from Cheiracanthium species, the evidence for a similar reaction in humans is unclear.
Authored by: Steve Jacobs, Sr. Extension Associate
March 2002 Revised 2015
Baerg, W. J. 1936. The Black Widow. Ark. Agr. Expt. Sta. Bul. 325. 34 pp.
Baerg, W. J. 1959. The Black Widow and Five Other Venomous Spiders in the United States. Ark. Agr. Expt. Sta. Bul. 608. 43 pp.
Bradley, R. A. 2013. Common Spiders of North America. University of California Press. 271 pp.
Breene, R. G., et al. 2003. Common Names of Arachnids. 5th ed. The American Arachnological Society Committee on Common Names of Arachnids. 42 pp.
Gertsch, W. J., and F. Ennik. 1983. “The spider genus Loxosceles in North America, Central America, and the West Indies (Araneae, Loxoscelidae).” Bul Amer Mus. Nat. Hist. 175: 24–360.
Herms, W. B., and M. T. James. 1961. Medical Entomology. 5th ed. The MacMillan Company, New York. 616 pp.
Howell, W. M., and R. L. Jenkins. 2004. Spiders of the Eastern United States: A Photographic Guide. Pearson Education. 363 pp.
Isbister, G. K., and M. R. Gray. 2003. “Effects of envenoming by combfooted spiders of the genera Steatoda and Achaearanea (Family Theridiidae: Araneae) in Australia.” J. Toxicol. Clin. Toxicol. 41: 809–819.
Kaston, B. J. 1948. “Spiders of Connecticut.” Conn. State Geol. Nat. Hist. Survey. Bull. 70. 874 pp.
Kaston, B. J. 1972. How to Know the Spiders. 3rd ed. Wm. C. Brown Company, Dubuque, Iowa. 272 pp.
Levi, H. W. 1959. “The Spider Genus Latrodectus (Araneae, Theridiidae).” Trans. Amer. Microscopical Soc. 78(1): 7–43.
Long, D., R. Snetsinger, and K. F. Helm. 1995. “Localized Pruritic Rash Due to Recurrent Spider Bites.” J. Geriatr. Dermatol. 3(6): 186–190.
McKeown, N., R. S. Vetter, and R. G. Hendrickson. 2014. “Verified spider bites in Oregon (USA) with the intent to assess hobo spider venom toxicity.” Toxicon 84: 51–55.
Ubick, D., P. Paquin, P. E. Cushing, and V. Roth, eds. 2005. Spiders of North America: An Identification Manual. American Arachnological Society. 377 pp.
Vetter, R. S., and P. Kirk Visscher. 1998. “Bites and Stings of Medically Important Venomous Arthropods.” International. J. Derm. 37: 481–496.
Vetter, R. S., et al. 2006. “Verified Bites By Yellow Sac Spiders (Genus Cheiracanthium) in the United States and Australia: Where Is the Necrosis?” Amer. J. Trop. Med. Hyg. 74(6): 1,043–1,048.
Vetter, R. S., and G.K. Isbister. 2008. “Medical aspects of spider bites.” Annu. Rev. Entomol. 53: 409–429.
Penn State College of Agricultural Sciences research, extension, and resident education programs are funded in part by Pennsylvania counties, the Commonwealth of Pennsylvania, and the U.S. Department of Agriculture.
Visit Penn State Extension on the web: http://extension.psu.edu
Where trade names appear, no discrimination is intended, and no endorsement by Penn State Cooperative Extension is implied.
This publication is available in alternative media on request.
Penn State is an equal opportunity, affirmative action employer, and is committed to providing employment opportunities to minorities, women, veterans, individuals with disabilities, and other protected groups. Nondiscrimination.
© The Pennsylvania State University 2017