Joseph Berger, Bugwood.org
Amaurobius and Callobius species
The Amaurobiidae superficially resemble the previous spiders, the funnel weavers, in the family Agelenidae. In fact, two genera in Agelenidae, Coras and Wadotes, have recently been transferred to the amaurobiids, bringing the number of genera in this family to thirteen.
Amaurobiidae have eight eyes that are similar in size, are typically of light (or white) color, and are arranged in two rows. The females range from 5 to 14 millimeters in length and the males from 5 to 12.5 millimeters. The carapace is a reddish, mahogany brown, darkest at the front in the region of the eyes and the chelicerae. The legs are lighter in color than the carapace. The abdomen is generally gray, although the background color varies from a pinkish flesh color to a dark, charcoal gray. A pattern of lighter areas or spots (which sometimes run together) can produce a larger, lighter central area. It is common to have chevron-type lighter areas on the posterior portion of the abdomen.
The web is an irregular "mesh" with an ill-defined tube retreat in the areas previously described.
Callobius and Amaurobius species have similar life histories and behaviors. They are most often found in damp locations under bark, leaf litter, and stones, as well as in woodpiles and other protected areas.
The males overwinter as immature spiders, molt twice the following spring, and become adults in April. They die after mating. The females have been found during all seasons, indicating that they probably live for at least two years. The egg sacs are deposited in the same locations that the spiders are found—often in the webs. The numbers of eggs found in the cocoons range from 73 to 175.
These spiders are frequently found in damp basements and other areas of the home in the autumn. However, there are few indications that these spiders will readily bite or that the bites are medically important. The one verified record of a bite by an immature Callobiusspecies resulted in pain, itching, swelling, redness, and nausea.
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.
Authored by: Steve Jacobs, Sr. Extension Associate
March 2002 Revised 2015